Detailed Design Project
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Detail Design of Wastewater Treatment Plant Research · October 2015 DOI: 10.13140/RG.2.1.3503.4327
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Design Project 2: DESIGN OF A SEWAGE TREATMENT PLANT | keshav soomaree
DESIGN PROJECT 2: DESIGN OF A SEWAGE TREATMENT PLANT
University of Mauritius Faculty of Engineering Department of Chemical and Environmental Engineering 4/3/2015
keshav soomaree 1114132 Coordinator: Mr A.K Ragen Project supervisor: Mr A Mudhoo Student Group: 3A
Table of Contents List of Tables & Figures: ...................................................................................................................... 6 Acknowledgment ................................................................................................................................. 8 List of abbreviations ............................................................................................................................ 8 CHAPTER 1: INTRODUCTION ...................................................................................................... 13 1.1
Aims and Objectives .......................................................................................................... 13
1.2
Summary of starting points for the detailed design ..................................................... 15
Summary of Preliminary mass balances ................................................................................. 15 Summary of preliminary Sizing of equipment ...................................................................... 16 1.3
Description of the wastewater treatment plant’s processes ......................................... 24
Screens ......................................................................................................................................... 24 Oil and Grease Removal............................................................................................................ 24 Equalization Tank ...................................................................................................................... 25 Circular Primary Settling Tank ................................................................................................ 25 The Membrane Bioreactor......................................................................................................... 25 Sand Filter ................................................................................................................................... 26 Chlorination ................................................................................................................................ 26 Thickener ..................................................................................................................................... 26 Sludge Digester .......................................................................................................................... 27 Dewatering Tank ........................................................................................................................ 27 1.4
Process Flow of Proposed Wastewater ........................................................................... 27
1.5
Key findings of the preliminary design .......................................................................... 29
1.6
Job allocation to other members ...................................................................................... 30
CHAPTER 2: Detailed Design .......................................................................................................... 30 2.1
Introduction ........................................................................................................................ 30
2.2
Design Calculations for the MBR ..................................................................................... 33
2.3
Determination of Calculated Parameters ....................................................................... 45
Pressure Calculations ................................................................................................................ 45 Flux Calculation ......................................................................................................................... 46 Temperature Correction ............................................................................................................ 46 Specific Flux ................................................................................................................................ 46 Salt Rejection ............................................................................................................................... 46 Sludge Retention Time .............................................................................................................. 47
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Recycle Ratio ............................................................................................................................... 47 2.4
Sizing of the MBR............................................................................................................... 47
2.5
Summary ............................................................................................................................. 49
2.6
Oil-Water separator design............................................................................................... 50
Horizontal Velocity (vH) ............................................................................................................ 52 Minimum Vertical Cross-Sectional Area (Ac) ........................................................................ 52 Channel Width and Depth ........................................................................................................ 53 Separator Length ........................................................................................................................ 53 Minimum Horizontal Area ....................................................................................................... 54 Maintenance ................................................................................................................................ 55 Construction Details .................................................................................................................. 56 Terminal Velocity of Oil Globules in Water ........................................................................... 57 Size and Gravity of Oil Globules ............................................................................................. 59 Derivation of Equation for Separator Length ........................................................................ 59 Calculation and results .............................................................................................................. 60 2.7
PIPE SELECTION AND PIPE SIZING FOR MBR TANKS OUTLETS AND INLETS 63
Pipe Selection .............................................................................................................................. 63 PE (Polyethylene) pipes ............................................................................................................ 64 PVC (Polyvinyl chloride) pipes................................................................................................ 65 Pipe sizing ................................................................................................................................... 65 Calculations................................................................................................................................. 66 2.8
Pump selection for MBR ................................................................................................... 67
2.9
Power requirements for pumps in MBR ......................................................................... 68
Pressure drop in pipelines ........................................................................................................ 69 Miscellaneous pressure losses .................................................................................................. 70 Summary of results .................................................................................................................... 71 CHAPTER 3: Heat and material Balance ........................................................................................ 72 3.1
Material Balance for the MBR........................................................................................... 72
3.2
Energy Balance ................................................................................................................... 77
Heat transfer during cooling .................................................................................................... 77 Analysis of system ..................................................................................................................... 78 Chapter 4:
Mechanical sketches and schedules......................................................................... 79
Chapter 5:
Material of Construction .......................................................................................... 84
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5.1
Material of construction for the membrane Bio-reactor Tank ..................................... 84
5.2
Material of construction for the module membrane ..................................................... 84
5.3
Material of construction for the oil-water separator ..................................................... 87
CHAPTER 6: Instrumentation and Control.................................................................................... 89 6.1
Control Strategies for the Membrane Bio-reactor.......................................................... 89
Process control and software .................................................................................................... 89 Pre-treatment and residuals management ............................................................................. 89 Tank sizing and redundancy .................................................................................................... 90 CHAPTER 7: Safety Considerations ................................................................................................ 94 7.1
The oil-water separator ..................................................................................................... 94
7.2
The Membrane Bioreactor................................................................................................. 95
CHAPTER 8: Review of the final design......................................................................................... 95 8.1
Summary of key Deviations ............................................................................................. 95
8.2
Review of API Separator ................................................................................................... 96
8.3
Review of the membrane bioreactor ............................................................................... 96
CHAPTER 9: ECONOMICS OF THE PROJECT, AS DESIGNED ............................................... 98 9.1
Total purchase equipment cost ........................................................................................ 98
9.2
Total capital investment (TCI) .......................................................................................... 98
9.3
Total product cost .............................................................................................................. 99
9.4
Total revenue ...................................................................................................................... 99
9.5
Gross earning cost .............................................................................................................. 99
9.6
Pay-back period ................................................................................................................ 100
9.7
The rate of return ............................................................................................................. 100
9.8
The Net Present Value (NPV) and Initial Rate of Return (IRR)................................. 100
CHAPTER 10: Environmental Concerns..................................................................................... 102 CHAPTER 11: Conclusion............................................................................................................. 103 References ......................................................................................................................................... 104 Appendices ....................................................................................................................................... 108 Appendices A: Mass Balance.......................................................................................................... 108 Mass Balance for the MBR .......................................................................................................... 108 Overall Balance around the MBR .......................................................................................... 108 BOD Balance around MBR ..................................................................................................... 110 Flow Balance ............................................................................................................................. 111 Solid Balance on membrane ................................................................................................... 111
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Balance on VSS on membrane ................................................................................................ 111 NH3-N Balance on the membrane skid ................................................................................. 111 NO3-N Balance on membrane skid........................................................................................ 112 Phosphorus Balance on the membrane skid ........................................................................ 113 Appendix B: Energy Balances ...................................................................................................... 113 Power requirement for the Membrane Bioreactor .................................................................. 113 Energy Balance on Aeration Tank ......................................................................................... 113 Energy Balance on membrane bio filter ................................................................................ 114 Energy balance on the amount of pumps ............................................................................. 115 Energy production from biogas ............................................................................................. 115 Appendix C: SIZING ..................................................................................................................... 116 Sizing of the MBR......................................................................................................................... 116 Sludge age or sludge retention time ...................................................................................... 116 Feed to microorganism ratio................................................................................................... 116 Total aeration volume and dimensions of the MBR tank ................................................... 117 Aeration Period or Hydraulic Retention time...................................................................... 118 Appendix D: Costing ....................................................................................................................... 120 Purchased Equipment Table....................................................................................................... 120 Bar screen ...................................................................................................................................... 124 API.................................................................................................................................................. 124 Rapid Mixing Tank ...................................................................................................................... 124 Flocculation Tank ......................................................................................................................... 125 Primary clarifiers .......................................................................................................................... 125 Calculating cost of equipment:............................................................................................... 125 Calculating present cost of equipment:................................................................................. 125 Cost index values: .................................................................................................................... 126 Cost estimation of Primary Clarifiers and Pumps............................................................... 126 Primary Clarifiers..................................................................................................................... 126 Pumps ........................................................................................................................................ 127 Cost estimation of Centrifuge................................................................................................. 127 Cost of Ancillaries .................................................................................................................... 127 COMPUTING THE TOTAL CAPITAL INVESTMENT ......................................................... 128 Calculating the total product cost .............................................................................................. 129 Computing the general expenses............................................................................................... 131
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Calculations for depreciation cost ............................................................................................. 132 Computing the total income ....................................................................................................... 133 Computing the gross profit ........................................................................................................ 134 Computing the payback period ................................................................................................. 134 Calculating Rate of Return .......................................................................................................... 134 Calculating Net Present Value (NPV) ....................................................................................... 134 Calculating Internal Rate of Return (IRR) ................................................................................ 136 Discounted Payback Period ........................................................................................................ 138
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List of Tables & Figures: 1TABLE 1.2.1: SUMMARY OF MASS BALANCE FOR SEWAGE FLOW OVER THE SYSTEM ........... 15 2TABLE 1.2.2.1: THE OIL-WATER SEPARATOR ........................................................................................ 16 3TABLE 1.2.2.2: BAR SCREEN ........................................................................................................................ 17 4TABLE 1.2.2.3: FINE SCREEN ....................................................................................................................... 18 5TABLE 1.2.2.4: EQUALIZATION TANK ..................................................................................................... 18 6TABLE 1.2.2.5: PRIMARY CLARIFIER ......................................................................................................... 19 7TABLE 1.2.2.6: THE MEMBRANE BIOREACTOR ..................................................................................... 20 8TABLE 1.2.2.7: SAND FILTER ....................................................................................................................... 21 9TABLE 1.2.2.8: CHLORINATION ................................................................................................................. 21 10TABLE 1.2.2.9: THICKENER ........................................................................................................................ 22 11TABLE 1.2.2.10: SLUDGE DIGESTER ......................................................................................................... 22 12TABLE 1.2.2.11: DEWATERING TANK ..................................................................................................... 23 13TABLE 1.5: KEY FINDINGS OF THE PRELIMINARY DESIGN ............................................................ 29 14TABLE 1.6: JOB ALLOCATION OF GROUP MEMBERS ........................................................................ 30 15FIGURE 2.1: EUROPEAN MEMBRANE BIOREACTOR MARKET ....................................................... 31 16TABLE 2.1: BIOLOGICAL OPERATING PARAMETERS ....................................................................... 33 17TABLE 2.2: FEED IN MBR ............................................................................................................................ 39 18TABLE 2.4: KINEMATIC CONSTANTS .................................................................................................... 39 19TABLE 2.5: BIOLOGICAL OPERATING PARAMETERS ....................................................................... 40 20TABLE 2.6: MEMBRANE OPERATING DATA ........................................................................................ 40 21TABLE 2.7: AERATION OPERATING DATA .......................................................................................... 40 22TABLE 2.8: BIOLOGICAL PARAMETERS ................................................................................................ 41 23TABLE 2.9: SLUDGE YIELD ........................................................................................................................ 41 24TABLE 2.10: MEMBRANE CALCULATIONS .......................................................................................... 42 25TABLE 2.11: MEMBRANE OPERATION................................................................................................... 42 26TABLE 2.12: AERATION DESIGN .............................................................................................................. 42 27TABLE 2.13: POWER REQUIREMENT ...................................................................................................... 43 28FIGURE 2.1: SPECIFIC COST VS. FLUX FOR HS AND FS TECHNOLOGIES, FLUX TO BE RELATED TO AERATION DEMAND ...................................................................................................................... 44 29FIGURE 2.3: SPECIFIC COST VS. AERATION DEMAND OVER THE RANGES OF AERATION DEMAND OBSERVED IN PRACTICE FOR HF AND FS TECHNOLOGIES .................................. 44 30FIGURE 2.4: DESIGN VARIABLES FOR OIL INTERCEPTORS. ............................................................ 51 31FIGURE 2.5: RECOMMENDED VALUES OF F FOR VARIOUS VALUES OF VH/VT ...................... 54 32FIGURE 2.6: SKETCH OF PARALLEL PLATE SEPARATOR - CROSS-FLOW ................................... 57 33TABLE 2.14: FLUID DENSITY AND VELOCITY ..................................................................................... 66 34TABLE 2.15: PUMP TYPES AND MAJOR APPLICATIONS IN WASTEWATER TREATMENT ..... 67
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37TABLE 2.17: SUMMARY OF RESULT INVOLVING THE MAIN PIPELINE CONNECTING THE MBR ............................................................................................................................................................ 71 38TABLE 3.1: ENTHALPY OF DIFFERENT GAS COMPONENTS ........................................................... 78 39TABLE 5.2.1: MEMBRANE CONFIGURATION DEFINITIONS ............................................................ 85 40TABLE 5.2.2: MEMBRANE MODULE DETAILS OF FS .......................................................................... 85 41TABLE 5.2.3: MEMBRANE MODULE DETAILS OF HF ......................................................................... 86 42FIGURE 5.3.1: STAINLESS STEEL OIL-WATER SEPARATOR.............................................................. 88 43TABLE 9.0: SUMMARY OF THE ECONOMICS OF THE TREATMENT POWER PLANT ............. 101
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Acknowledgment I wish to thank Mr. Ackmez Mudhoo, our design coordinator, for guiding us and giving us all the possible help that he could. I am thankful to him since he was always present when we needed him and was here to direct us to the right way. I am also grateful to Mr. Arvinda Ragen, our program coordinator, who ensured that we did not lack anything with regards to the project and he did his best to give us all the facilities we needed. I would also like to thank Dr. Dinesh Soorup, the head of department, who responded positively to all the problems faced by us.
List of abbreviations ABR
Anaerobic baffled reactor
Ac
total cross section, m2
AD
Anaerobic digestion
ADUF
Anaerobic digester ultrafiltration
AH
total surface area, m2
Alum
Aluminum [aluminium?] sulphate
AN
Anaerobic
anMBR
Anaerobic membrane bioreactor
AOC
Assimilable organic carbon
ASP
Activated sludge process
AX
Anoxic
B
width of one channel, m
BAC
Biologically activated carbon
BAF
Biological aerated filter
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BNR
Biological nutrient removal
BOD
Biochemical oxygen demand
BPA
Biological potential activity
CEB
Chemically-enhanced backwash
CF
Crossflow
CFV
Crossflow velocity
CIL
Cleaning in line
CIP
Cleaning in place
COD
Chemical oxygen demand
CP
Concentration polarisation
CPR
Chemical phosphorous removal
CST
Capillary suction time
CT
Capillary tube
d
depth of water in channel, m
Da
Dalton
DE
Dead-end (or full flow)
dMBR
Diffusive membrane bioreactor
DO
Dissolved oxygen
DOC
Dissolved organic carbon
DS
Dry solids
EBPR
Enhanced biological phosphate removal
EGSB
Expanded granular sludge bed
eMBR
Extractive membrane bioreactor
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F:M
Ratio Food-to-micro-organism ratio
FBDA
Fine bubble diffusion aeration
FC
Filter cartridge
Flocs
Flocculated particles
FS
Flat sheet (or plate-and-frame)
GAC
Granular activated carbon
GLD
Gigalitres per day
GT
Gas transfer
HF
Hollow fibre
HPSEC
High performance size exclusion chromatography
HRT
Hydraulic retention time
ID
Internal diameter
iMBR
Immersed membrane bioreactor
kDa
kiloDalton
L
length of channel, m
LMH
Litres per m2 per hour
LMH/bar
Litres per m2 per hour per bar
MABR
Membrane aeration bioreactor
ME
Membrane extraction
MF
Microfiltration
MHBR
Membrane hydrogenation bioreactor
MLD
Megalitres per day
MLSS
Mixed liquor suspended solids
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MLVSS
Mixed liquor volatile suspended solids
MPE
Membrane performance enhancer
MT
Multitube
MW
Molecular weight
MWCO
Molecular weight cut-off
n
number of channel
NADH
Nictotinamide adenine dinucleotide hydrogenase
NF
Nanofiltration
NOM
Natural organic matters
O&M
Operation & Maintenance
OC
Organic carbon
OD
Outer diameter
OLR
Organic loading rate
ON
Organic nitrogen
OTR
Oxygen transfer rate
OUE
Oxygen utilisation efficiency
p.e.
Population equivalent
PAC
Powdered activated carbon
PAN
Polyacrylonitrile
PE
Polyethylene
PES
Polyethylsulphone
PP
Polypropylene
PV
Pervaporation
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PVDF
Polyvinylidene difluoride
Qm
Flow of oily water into the oil-water separator, m3/s
RBC
Rotating biological contactor
Rc
Cake resistance
Redox
Reduction-oxidation
rMBR
(Biomass) rejection membrane bioreactor
RO
Reverse osmosis
SAD
Specific aeration demand
SADm
Specific aeration demand – membrane area
SADp
Specific aeration demand – permeate volume
SAE
Standard aeration efficiency (kgO2/kWh)
SBR
Sequencing batch reactor
SCADA
Supervisory control and data acquisitions
SDI
Silt density index
sMBR
Sidestream membrane bioreactor
SMP
Soluble microbial product
SMPc
Soluble microbial product (carbohydrate)
SMPp
Soluble microbial product (protein)
SNdN
Simultaneous nitrification/denitirification
SRF
Specific resistance to filtration
SRT
Solids retention time
SVI
Sludge volume index
SW
Spiral-wound
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TDS
Total dissolved solids
TF
Trickling filter
THMFP
Tri-halo methane formation potential
TKN
Total Kjedldahl nitrogen
TMDL
Total maximum daily load
TMP
Transmembrane pressure
TOC
Total organic carbon
TSS
Total suspended solids
UF
Ultrafiltration
VH
horizontal flow velocity, m/s
VRM
Vacuum rotating membrane
VSS
Volatile suspended solids
Vt
rise rate of oil globule, m/s
WRP
Water recycling (or reclamation) plant
WWTP
Wastewater treatment plant
CHAPTER 1: INTRODUCTION Sewage is a major carrier of disease and toxins .The safe treatment of sewage is thus crucial to the health of any community. This Project focuses on the complex physical and biological treatments used to render sewage both biologically and chemically harmless. 1.1
Aims and Objectives
The design project consists of two parts namely a ‘Preliminary report’ (Design Project 1) and a ‘Detailed report’ (Design Project 2). This detailed design is a follow up of the previous preliminary design conducted and it deals with the review of all the limitations of the design 1. The results obtained previously are fine-tuned and
Page | 13
mechanical designs of the major equipment are prepared. In Mauritius, rapid population growth and unplanned development are contributing to rapid depletion of per capita water availability. Moreover, a limited amount of rainfalls accompanied with a high rate of evaporation and redundant habit of wasting water of the population; even though severe dry season prevailing are the breeding factors for water shortage. Similarly, with an annual swell of 3% in the volume of water injected into the distribution system during the past 20 years, has shot the daily water consumption per capita from 152 liters in 1990 to 216 liters in 2013(Digest of Energy and Water Statistics, 2013) and many are convinced that we are just a few drops away from the “Water Scarce” status. Thus, there was an urgent need for a strategic plan that tackle this issue. Likewise, more emphasis is being laid on preservation and protection of environment while the government came forward with an excellent strategic plan; National Sewerage Project (NSP, 2011), set up to solve at one go the water scarce. Opting for wastewater treatment ensures that not much great demands are been made on the environment in Mauritius, therefore it is a step forward towards safeguarding the ecological and marine resources, in particular surf water and ground water and as well as improve sanitation and protect public health. In addition, the opting for wastewater treatment and reuse makes provision for long term water reliability within the community by providing substitute for fresh water and also is a plus-point for water demand and drought management in overall water resources planning. Likewise, reuse of wastewater also enables the allocation of good quality fresh surface water or ground water for higher value purposes, which can be either for human consumption or meeting domestic needs, thus also protecting existing sources of fresh water as it obviate the requirement of mobilization of additional resources to increasing demand. On the other hand, one of the aims of this project is to study the feasibility of implementing a wastewater treatment plant for an industrial wastewater possessing certain specified characteristics and simultaneously device certain processing strategies that will enable compliance of the treated water with the irrigation norms.
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The objective of the detailed design project is intended to bring together the knowledge and skills that have been assimilated through the B Eng. (Hons) Chemical & Environmental Engineering undergraduate course and to demonstrate creative and critical powers in making decisions in areas of uncertainty. 1.2
Summary of starting points for the detailed design
The Detailed Design Project will be started based upon values of the preliminary design. The limitations which are revised in this report are also listed. Summary of Preliminary mass balances 1Table 1.2.1: Summary of mass balance for sewage flow over the system
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Table 1.2.1(continued)
Summary of preliminary Sizing of equipment 1.2.1.1 The Oil-Water Separator 2Table 1.2.2.1: The oil-water separator
Vertical Velocity
0.18083 cm/s
Horizontal flow velocity
1.5 cm/s
minimum vertical cross-sectional area
54 m2
number of channels
2
Page | 16
Width of channel
8m
Depth of channel
3.38 m
Length of channel
3.33 m
Limitation: The system was designed assuming that only free oil is present in the effluent, other types of oil may be present which may affect the efficiency of the system. 1.2.1.2 Bar Screen 3Table 1.2.2.2: Bar screen
Depth of chamber, d
1.50 m
Total width of opening at the rack, w
0.6m
Clear bar spacing
50 mm
Number of bars
12
Width of bar
10 mm
Thickness of bar
50 mm
Width, W of the chamber
0.72 m
Height of rack( allowing 0.6 m of freeboard)
2.0 m
Angle of inclination of the bars to the horizontal, θ
80˚
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1.2.1.3 Fine screen 4Table 1.2.2.3: Fine screen
Depth of chamber, d
2m
Total width of opening at the rack, w 0.45 m
Clear bar spacing
9.5 mm
Number of bars
48
Width of bar
10 mm
Thickness of bar
50 mm
Width, W of the chamber
0.93 m
Height of rack( allowing 0.6 m of freeboard) Angle of inclination of the bars to the horizontal, θ
2.63 m
80˚ Mainly of stainless steel for protection
Material of construction
against corrosion and for higher lifetime
1.2.1.4 Equalization Tank 5Table 1.2.2.4: Equalization Tank
Number of Equalization tank
3
Flow rate per tank, Q (m3/h)
967.87 m3/h
Retention time (hours)
3 hours
Area (m2)
556.42 m2
Volume (m3)
3,338.52 m3
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Length (m)
33.36 m
Breadth (m)
16.68 m
Freeboard (m)
0.5 m
Inlet velocity (m/h)
1.73 m/h
Material of construction
Concrete
Limitations: 1. The effluent was assumed to have an overall constant mass loading which is practically impossible in reality. 2. The tank was assumed to be constant volume basin, again since no interior slope was provided it is impossible to be achieved. 3. The assumptions and calculations yield a large volume of equalization tank which is may not be required. 1.2.1.5 Primary Clarifier 6Table 1.2.2.5: Primary Clarifier
Number of tank
2 clarifiers in parallel
Flow rate per tank, Q (m3/h)
1458.3
Retention time (hours)
2.5
Area (m2)
1000
Volume (m3)
3646
Tank Diameter (m)
36
Height (m)
3.65
Material of construction
Concrete
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1.2.1.6 The Membrane Bioreactor 7Table 1.2.2.6: The membrane Bioreactor
Shape
Rectangular
Total volume
14934 m3
Dimensions (L x B x H)
42.5m × 88 m × 4.4 m
Number Of channels
20 channels
Material
reinforced concrete
Water temperature
28 0C brought to 20 0C
Liquid depth
7m Fine bubble ceramic diffuser
Aeration system
Oxygen
demand
=
1565.40 𝑚3 𝑜𝑓 𝑂2⁄𝑑𝑎𝑦 Aeration period
5.12 ℎ𝑜𝑢𝑟𝑠
Diffuser submergence
7m
Oxygen transfer efficiency (OTE)
35%
Aeration configuration
Covering the floor completely Using a centrifugal blower
Air supply
feeding 7454.24 𝑚3 𝑜𝑓 𝑎𝑖𝑟⁄𝑑𝑎𝑦
SRT
10 days
BOD vol. loading F/M
0.938
𝐾𝑔 𝑚3 . 𝑑𝑎𝑦
0.3
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1.2.1.7 Sand Filter 8Table 1.2.2.7: Sand Filter
Number of sand filter
1
Flow rate/ sand filter, Q (m3/h)
69,674 m3/day
Area (m2)
87.5 m2
Breadth (m)
9.35 m
Length (m)
9.35 m
Volume (m3)
305.98 m3
Under drain depth (m)
0.8 m
Filtration duration (h)
20 hours (per day) Reinforced concrete is used
Material of construction
for the tank with the filter media being sand.
1.2.1.8 Chlorination 9Table 1.2.2.8: Chlorination
Number of tank
4
Flow rate of NaOCl /channel, Q
0.00564 m3/s
Volume of 1 tank
362.9 m3
Volume of 4 tanks
1,451.5 m3
Depth
1.8 m
Breadth
2.2m
Cross sectional area
3.96 m2
Length
91.6 m
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Length of each channel
30.5 m
1.2.1.9 Thickener 10Table 1.2.2.9: Thickener
Number of thickeners
2
Volume (m3)
956.12 m3
Surface area (m2)
152.59m2
Diameter (m)
13.94 m
Side water depth (m)
5.8 m
Depth at central hopper (m)
7.19 m
Thickening period (days)
3.48 days
Total flow (m3/d)
548.94 m3/d Reinforced concrete for tank while inner
Material for construction
equipment are of stainless steel, resistant to corrosion
1.2.1.10 Sludge Digester 11Table 1.2.2.10: Sludge Digester
Number of digesters
2
Volume (m3)
2019.6 m3
Area (m2)
176.71m2
Diameter (m)
15 m
Side wall height (m)
13.22 m
Central hopper depth (m)
14.72 m
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Amount of VSS in thickened sludge (Kg /d)
13511.96 Kg/d Reinforced concrete is used for the digesters
Material for construction
while
any
other
equipment is made up of stainless steel.
1.2.1.11 Dewatering Tank 12Table 1.2.2.11: Dewatering Tank
FIRST TANK Number of tank
1
Surface area
1.85 m2
Volume designed
1.92 m x 0.96 m x 1m + 0.5m (freeboard)
Total solids flowrate
763 kg/hr
total amount of polymer used Material for construction
2.771 kg/hr Fiber glass is used. Inox stainless steel is chosen the stirrer.
MATURATION TANK Number of tank
1
Volume designed
1.85m3
Surface area
1.85 m2
Flow
rate
solution
of
polymer
17.08 m3 /hr
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Material for construction
1.3
Fiber glass is used. Inox stainless steel is chosen the stirrer
Description of the wastewater treatment plant’s processes
Industrial wastewater treatment encloses various mechanisms and processes used to treat water that have been contaminated in some way by anthropogenic industrial or commercial activities prior to its release into the environment or its re-use. Similar the mechanisms or processes to be employed to treat the water is chiefly dependent on the characteristics of the water and depend on the subsequent possible reuse of the water. Thus the treatment facility has designed to treat the effluent to comply with the irrigation norms and in subsequent text below provide an overview of different system employed. Screens A screen is a device with openings, generally of uniform size, that is used to retain solids found in effluent wastewater (Metcalf and Eddy, 2004) and often the first unit operation in wastewater treatment plant. Basically screens can be classified by two methods; firstly by their method of cleaning: hand cleaned or mechanically cleaned and secondly by the size of their clear openings: coarse, medium and fine screens. Likewise in our case, the wastewater will pass through a climber type mechanically raked screen for the removal of coarse screens since the designed flow-rate is considerably large. Oil and Grease Removal To start with, a simple assumption that was prompted while considering the design of the oil and grease separator; is that the total oil and grease concentration was due to the presence of free oil. The latter is in the form of discrete globules with size sufficient enough for its globules to rise as a result of buoyant forces forming an oil layer at the water surface. Free oil can be removed under proper quiescent conditions by gravity method. Thus in the case of our design we will go for the API gravity separator due to the fact that it has been successfully been used in refineries for many years (Kirby S. Mohr 2001). The basic design of an oil water separator is a long
Page | 24
rectangular basin with a detention time of about 30 minutes (Metcalf and Eddy, 2004) with an efficiency of 92%. Most of these separators are divided into more than one bay and are usually equipped with scrapers to move the oil downstream where it is collected on a drum. The sludge produced can be dewatered, incinerated or disposed of in hazardous waste landfills. Equalization Tank In the preliminary design, assuming that the wastewater has an overall constant mass loading; and in line equalization tank was considered despite its constraints like larger volume requirement and higher operational cost due to continuous pumping of wastewater from the equalization since it offers a more uniform flow and strength of wastewater. Since the tank was placed just after the PST and with a short detention time so neither no mixing or aeration processes was provided as a control measure to avoid deposit solids or odor formation. Circular Primary Settling Tank Prior to the settling tank, there are the flocculation tanks and mixing tanks that will allow for the formation of flocks that will trap both the total suspended solids and the organic matter as biochemical oxygen demand present in the wastewater. This technique is referred as advanced sedimentation process and the mostly applied flocculent is alum. The settling tank can remove up to 80% of total suspended solids and 40% of the biochemical oxygen demand. A circular setting was selected since this allows for central feeding of wastewater to the top of the tank, therefore increasing favoring better settling of the flocks formerly produced. Sludge will be collected at the bottom of the tank and will be used, mixed with sludge from other units of the plant for the production of biogas. The Membrane Bioreactor There are essentially three main elements of a membrane bioreactor (MBR) contributing to operating costs, ignoring membrane replacement. These are: 1. Liquid pumping 2. Membrane maintenance 3. Aeration
Page | 25
Of these by far the most significant, especially for immersed technologies, is aeration. As already discussed in the primary design, aeration is used both for scouring an immersed membrane and for suspending and maintaining a viable biomass. Design of an MBR therefore demands knowledge both of the feed water quality, which principally determines the oxygen demand for bio-treatment, and the aeration demand for fouling control, which relates to a number system characteristics. Sand Filter Slow sand filters proved to be uneconomical when compared to rapid sand filters and micro screen where the efficiency reached were about 60 % for suspended solids (TSS) and about 40 % for BOD. Operation of a rapid sand filter consists of regular backwashing. The period between backwashes depends on the quality of the water being filtered. The purpose of backwashing is to remove the suspended material that has been deposited in the filter bed during the filtration cycle. Periodic repacking of the filter bed may be required at infrequent intervals to ensure efficient operation (Negulescu, 2011). Rapid sand filter are preferred compared to slow filter as back washing occurs rapidly and it has a high filtration rate of about 150 to 200 million gallons of water per acre per day. Chlorination The most frequent disinfectants are chlorine, ozone and UV rays UV rays, being highly effective for pathogen sterilization, are also very expensive. Ozone is highly toxic but not readily available. Considering the effects and inconveniences of UV rays and ozone, Chlorination is chosen, even though it is somehow toxic as it increases the total dissolved solids in the effluent, it is the less expensive one (Hung et al. 2012). It must be noted that due to the selection of the membrane bioreactor in our system, which has a very high initial cost, we need to minimize the cost for our other units. Thickener Gravity thickener is the most common type of thickener which can act as a thickener and achieve blending, important to produce a uniform mixture for subsequent processes at the same; thereby eliminating the need for a separate blend tank. This type of thickener is chosen since the solids concentration of 4 – 6 % achieved by a
Page | 26
gravity thickener that is required by the high rate digester. It requires the minimum power consumption compared to dissolved air flotation and centrifugal thickener. It also has the least operation skill requirement and operating costs. Conditioning chemicals and polymer are typically not needed as is the case for gravity belt thickener and rotary drum thickener. The pH can also be adjusted in this type of thickener which can provide space for storage (Metcalf and Eddy, 2003). Sludge Digester High rate digestion is deemed suitable for the process as it requires less space and short detention time of 10 – 30 days compared to low rate digestion. Mesophilic digestion is chosen since the operating temperature for these organisms is 30 – 38 0C; thus reducing less energy requirement compared to the thermophilic digestion where fluctuations in temperature can cause process instability and a risk of higher odor potential. Thermophilic and 2 stage digestion process produce a poorer quality supernatant which contains dissolved materials; requiring further special treatment. As for the 2-stage digestion process, it is still under pilot studies and will be more energy intensive; requiring 2 mixing devices for both tanks. Dewatering Tank The aim of the dewatering equipment is to achieve fifty percent by dry weight solids content and centrifuge equipment can produce the required percent. In addition, its capital cost is low when compared to other methods, there is minimization of odor as it is an enclosed unit and requires little supervision; thus continuous solid bowl centrifuge is chosen since it is more suited for high solid content and used for medium and large plants compared to imperforated basket centrifuge. Filter press has many inconveniences such as mechanical complexity; high chemical and labor costs and limitation on filter cloth life while vacuum filtration has low operational costs but higher initial costs and land requirements. 1.4
Process Flow of Proposed Wastewater
Next is the process flow diagram of proposed wastewater treatment
Page | 27
BS1:1st Bar Screen BS2:2nd Bar Screen RS: Raw Sewage PS: Primary Sludge
PC1: 1st Primary Clarifier PC2: 2nd Primary Clarifier GT: Gravity Thickener SD: Sludge Digester
CS: Clear Supernatant S: Screenings OGT: Oil & grease Trap AB: Air Blower
ET: Equalization Tank CD: Centrifuge Dewatering SF: Sand Filter EP: Electricity to Plant
BT: Bioreactor Tank MS: Membrane Skid LT: Landfill Truck CU: Chlorination Unit
TT: Transportation Truck WAS: Waste Activated Sludge EI: Effluent to Irrigation OG: Oil & Grease
AB
PC1
BT
BS1
MS
ET SF PC2
BS2 OGT PS
S OG
CS LT
WAS GT
FLOWLINE ANNOTATIONS Raw Sludge
Biogas
Oil & Grease
Electicity
Screenings
Filtered Effluent
Sewage
Air
Air Clear Supernatant
SD
EP
EG
Disinfected Effluent
Chlorine
CS
CD TT
Primary Sludge Waste Activated Sludge
Page | 28
1.5
Key findings of the preliminary design
13Table 1.5: Key findings of the preliminary design
Equipment Coarse 1
screens
(Inclined
QTY
Cost ( Rs) / unit
Total Cost / Rs
2
253,150
506,300
2
305,000
610,000
1
300,212.17
300,212
bar
screen with rack and pinion system- Infilco Degremont bar screen)
2
3
Fine bar screen (Fine straight bar screen GFD type) Rectangular in-line equalization tank equipped with mixer
4
Circular clarifier
2
23,082,825.07
46,165,650
5
MBR
1
3,536,920
3,536,920
1
226,441.24
226,441
1
40,371,838.51
40,371,839
1
6,955,415.34
6,955,415
6 7 8
Rapid Sand Filtration equipped with an inlet chamber Thickener Square
Based
UASB
digester
sludge
9
Centrifuge
1
2,003,400
2,003,400
10
Pumps
9
61,500
553,500
11
Oil separator
1
15,762,107.85
15,762,108
Total Purchase Equipment Cost
116,991,785
Net income = Rs 25,611,771.6 Payback period = 7 years
Page | 29
1.6
Job allocation to other members
14Table 1.6: Job allocation of group members
Wastewater Treatment – Group 3A Name
Equipment Allocated
RAMDHONEE A.K.R. Mishra
Gravity Thickener & Equalization Tank
SOOMAREE Keshav
Membrane Bioreactor(Major) & Oil-Water Separator(Minor)
RAMANAH R. Devi (Ms)
Sludge digester & Sand filter
ST PAUL M.M. Eldora (Ms)
Clarifier & dewatering unit
RAMDEWAR P. Kumar
Screening & Disinfection unit (Chlorination)
CHAPTER 2: Detailed Design Major: Design of the Aerobic Membrane Bioreactor. 2.1
Introduction
The progress of technological development and market penetration of membrane bioreactors (MBRs) can be viewed in the context of key drivers, historical development and future prospects. As a relatively new technology, MBRs have often been disregarded in the past in favor of conventional bio treatment plants. However, a number of indicators suggest that MBRs are now being accepted increasingly as the technology of choice. Market analyst reports indicate that the MBR market is currently experiencing accelerated growth, and that this growth is expected to be sustained over the next decade. The global market doubled over a 5-year period from 2000 to reach a market value of $217 million in 2005, this from a value of around $10 million in 1995. It is expected to reach $360 million in 2015 (Hanft, 2006). As such, this segment is growing faster than the larger market for advanced wastewater treatment equipment and more rapidly than the markets for other types of membrane systems. In Europe, the total MBR market for industrial and municipal users was estimated to have been worth €25.3 million in 1999 and €32.8 million in 2002 (Frost and Sullivan,
Page | 30
2003). In 2004, the European MBR market was valued at $57 million (Frost and Sullivan, 2005). Market projections for the future indicate that the 2004 figure is expected to rise annually by 6.7%; the European MBR market is set to more than double its size over the next 7 years (Frost and Sullivan, 2005), and is currently roughly evenly split between UK/Ireland, Germany, France, Italy, the Benelux nations and Iberia (figure 1.1) The future for the MBR market is thus generally perceived to be optimistic with, it is argued, substantial potential for growth. This level of optimism is reinforced by an understanding of the key influences driving the MBR market today and those which are expected to exert an even greater influence in the future. These key market drivers include greater legislative requirements regarding water quality, increased funding and incentives allied with decreasing costs and a growing confidence in the performance of the technology. 15Figure 2.1: European membrane bioreactor market
(Frost and Sullivan, 2005)
MBR Market 16%
19%
UK and Ireland Germany
19% 18% 16%
12%
France Italy Iberia Benelux
It appears to be true that traditionally decision-makers have been reluctant to invest the relatively high start-up costs required on a relatively new technology (15 years) which produces an output of higher quality than that required. This is especially so
Page | 31
when MBRs have historically been perceived as requiring a high degree of skill and investment in terms of operation and maintenance (O&M) with key operating expenditure parameters, namely membrane life, being unknown (Frost and Sullivan, 2003). Whilst robust to changes in loading with respect to product water quality, MBR O&M protocols are critically sensitive to such parameters because of their impact on the membrane hydraulics (i.e. the relationship between throughput and applied pressure). Whilst there are many examples of the successful application of MBRs for a number of duties, there are also some instances where unscheduled remedial measures have had to be instigated due to under-specification, inappropriate O&M and other factors generally attributable to inexperience or lack of knowledge. All of this has fed the perception that MBRs can be difficult to maintain. In the past there have been an insufficient number of established reference sites to convince decision-makers of the potential of MBRs and the fact that they can present an attractively reliable and relatively cost effective option. This is less true today, since there are a number of examples where MBRs have been successfully implemented across a range of applications, including municipal and industrial duties. In many cases the technology has demonstrated sustained performance over the course of several years with reliable product water quality which can, in some cases, provide a clear cost benefit. Lastly, developing new water technology, from the initial laboratory research stage to full implementation, is costly and time consuming (ECRD, 2006). This problem is particularly relevant considering that the great majority of water technology providers in Europe are small- and medium-sized enterprises (SMEs) that do not have the financial resources to sustain the extended periods from conception at laboratory scale to significant market penetration. Whilst the most significant barrier to the more widespread installation of MBRs remains cost, there are a number of drivers which mitigate this factor. Foremost of these is increasingly stringent environmental legislation relating to freshwater conservation and pollution abatement which has driven technological development in the water sector over the last 30–40 years. This, along with various governmental,
Page | 32
institutional and organizational incentives, has encouraged problem holders to appraise more sophisticated technologies such as MBRs in recent years. Moreover, both capital (and particularly membrane) and operational costs of the MBR process have decreased dramatically over the past 15 years, although further significant cost reductions may be unattainable unless membrane modules become standardized in the same way as has taken place for RO technologies. 2.2
Design Calculations for the MBR
16Table 2.1: Biological operating parameters
Raw data
Calculated data
Average
flow
(m3/day)
Q
specific
substrate Utilization µm/Y rate (kg/(g/day))
Peak
flow
(m3/day) BOD
Maximum
influent
(mg/L)
Qpeak
Effluent BOD (Sg/m3) Ks(1-Keθx)/ θx(YK-Ke)-1 Specific
S0
growth
of
nitrifying
1/θx
bacteria, µng/(g/day)
Biodegradable COD
(mg/L)
(often taken a 1.6
bCOD
Effluent nitrogen (Ne g/m3)
Kn(µn+Ke,n)/µn,m- Ke,n-µn
BOD) Total
suspended
solids
influent TSS
Cell debris ( fd g/g)
≈ VSS/S0
(mg/L) TSS
effluent
(mg/L) (normally TSSe negligible) Volatile suspended solids (mg/L)
VSS
Sludge
yield
(Px
g/day) Non-biodegradable solids (X0 g/day)
[QY(So-S)/(1+ Keθx)] – [fdKeQY θx(So-S)/
(1+
Keθx)]
[QYnNOx/(1+ Ke,nθx)] (TSS -VSS)Q
Page | 33
–
Wastewater
Tw
temperature (°C)
Sludge wastage flow (Qw m3/day) Observed yield, Yobs
SRT (day)
θx
mg VSS/(mg BOD day)
Design
mixed
liquor suspended MLSS solids (mg/L) Anoxic
tank
V m3 Food
as
percentage
Aerobic tank volume
of Va /Van
aerobic tank size
to
[Y/(1+ ke θx)] + [fd Ke Y θx/(1+ ke θx)]
Px θx/X
micro-
organisms ratio, F:M kg
V/ θx
BOD/(kg
SQ/VX
TSS/day)
Maximum specific growth
rate
(heterotrophic) (mg
µm
VSS/(mg
Oxygen requirement, Q [(So-S) - 1.42Px/Q + 4.33 NOxm0 kg/day
2.83NOx
VSS/day)) Saturation coefficient (heterotrophic)
Required airflow to Ks
(mg/L BOD)
meet
biological
requirements,
QA’,b
(RoXOTE)/(ρA0.21αβτ)
kg/day
Endogenous decay coefficient (heterotrophic), (mg
Ke
α factor
e-0.084.X
VSS/(mg
VSS/day) Yield
coefficient
(heterotrophic) (mg VSS/(mg BOD
Y
Sludge wastage, Qw m3/day
V/ θx
Page | 34
Maximum specific growth
rate
Sludge waste per unit
(nitrification), (mg µm,n
permeate
QW/J’netAm
VSS/(mg
(Qw,vm3/(m3day)
VSS/day)) Endogenous decay coefficient
Airflow
per
(nitrification) (mg Ke,n
permeate
VSS/(mg
m3/(m3/day))
unit (Rb QA,B/ ρA J’netAm
VSS/day)) Yield
coefficient
(nitrification), mg Yn VSS/(mg BOD)
Normalized
Raw data
or
derived
data
Mean flux (LMH)
J
Mean
Temperature-corrected
J/1.024 (T-20)
flux, J’, LMH Temperature-corrected
transmembrane
∆Pm
pressure (bar)
mean
permeability J’/∆Pm
(LMH/bar) Temperature,
Aeration rate (m3/h)
QA,m
corrected
pressure-
aeration
rate,
Q’A,m (m3/h) Temperature wastewater (K)
of
TW,K
Temperature-corrected net flux, J’net (LMH)
QA,m(293/
Ta,K)*(
Pa.l/101.323)
N[(J’ tb – J’ τb)/( tc + τc)
Page | 35
Membrane Inlet air temperature (K)
Ta,K
aeration
demand
per
membrane
area,
unit SADm
Q’A.m/A’m
(Nm3/(hm2)) Inlet
air
pressure
(kPa)
Membrane Pa.l
aeration
demand per unit permeate Q’A.m/J’Am flow, SADp Specific membrane aeration
Membrane area (m2)
Am
energy
demand,
Wb,V KQ’A.m/ ρaJ’Am
(kWh/m3) Physical
Specific hydraulic energy
cleaning(backflush)
tb
interval (h)
demand
for
membrane ∆P/ ρp
permeation, Wh (kWh/m3) Specific
Physical cleaning(backflush)
τb
duration (h)
recirculation
energy demand per unit permeate
volume,
Wp
RρbgH/1000 ξ
(kWh/m3) Mass of chemical reagent
Backflush flux (LMH) Jb
per unit permeate volume, cc vc/ J’net Am( tc + τc) Mc (kg/m3)
Cleaning interval (h)
tc
Cleaning duration (h) τc Cleaning
reagent
strength (kg/m3) Cleaning
reagent
volume (m3)
cc
vc
Density (kg/m3)
ρ
Pumping efficiency
ξ
Conversion
According to Metcalfe and Eddy (2003), pp. 709.
Page | 36
Sizing of the MBR Packing density given by ratio of fibre surface area to volume Φ = Af / V
Where
(1)
Af = surface area of fibres = Nπdf
(2)
V = module volume Av = volume occupied by fibres = Nπdf 2/4
(3)
So: Av/ Af = df / 4
(4)
Thus; Ax = (4V – df Af) / 4L
(5)
Where Ax = free x-sectional area So: QA = 3600U / 4L x (4V - – df Af)
(6)
Where QA = aeration rate in m3/hr U = air flow velocity in channels (m/s) SADm = 3600U / 4V x (4V/Af – df)
(7)
Where SADm = aeration demand with respect to fibre area Substituting for V/Af and normalizing against flux: SADp = 3.6x106U / 4LJ x (4/ Φ – df)
(8)
Where SADp = aeration demand with respect to permeate volume Evidence suggests that J is a linear function of aeration intensity: J = mU + c
(9)
Where m and c are empirical constants So: SADp = 3.6x106U / 4L (mU + c) x (4/ Φ – df)
(10)
Aeration energy demand in kWh/m3 permeate is then given by
Page | 37
EA = 0.0303 SADp γ x [((10x + 101) / 101)(1 – 1/ γ) – 1] / (γ – 1) ζ (11) Where γ = aerator constant = 1.4 ζ = blower efficiency = 0.5 x = aerator depth = 3 m So: EA = Uk / L (mU + c) x (4/ Φ – df)
(12)
Where K = 0.0303 x 3.6x106 / 4 x γ x [((10x + 101) / 101) (1 – 1/
γ)
– 1] / (γ – 1) ζ and is thus
constant for a given system. Now, commercial technical data for available membrane modules (Judd, 2006) suggests that, for packing density and fiber diameter respectively in m-1 and m: 1 / Φ ≈ gdf + 0.001 f
(13)
Where f = 0.7-1.7 and g = 0.9-1.1 Thus EA = Uk / L (mU + c) x [(4/g-1) df + 0.004f)
(14)
For the four main MBR HF membrane suppliers, g = 0.89 (R2 = 0.97) and f = 1.7, and thus: EA = Uk / L (mU + c) x [3.5 df + 0.0068]
(15)
Design calculation A complete design for an immersed membrane bioreactor (iMBR) can be carried out on the basis of the information presented, provided the nature of the interrelationship can be determined between aeration and: (a) Permeability and cleaning protocol for the membrane permeation component,
Page | 38
(b) Feed water quality, flows and bio kinetics for the biological component. 17Table 2.2: Feed in MBR
Parameter
Value
Units
Q
50,000
m3/day
Qp
203384
L/H
Qpeak
1000
L/H
BOD So
220
g/m3
COD
430
g/m3
BOD:COD ratio
1:2
TSS
250
g/m3
VSS
190
g/m3
N
40
g/m3
Non-biodegradable VSS
0.24
g/gTSS
TW
12
oC
TW,K
285
oK
Ta
15
oC
Ta,K
288
oK
Pa,I
101
kPa
ρa
1.23
Kg/m3
ρb
1003
Kg/m3
ρp
996
Kg/m3
18Table 2.4: Kinematic constants
BOD Parameter
Ammonia Values
Unit
Parameter
Values
Unit
Ks
60
g/m3
µm,n
0.41
g/(g/day)
Ke
0.06
Per day
Kn
0.05
g/m3
Y
0.4
g/gBOD
Kdn
0.07
g/(g/day)
T = 20 oC
Page | 39
µmax
4.7
g/(gVSS/day) Yn
0.13
g/(g/day)
fd
0.86
gnbSS/gfeed
0.040
g/(g/day)
Yobs
0.64
g/gBOD
µn
According to Metcalfe and Eddy (2003), pp. 709. 19Table 2.5: Biological Operating Parameters
Parameter
Values
Unit
X
8000
g/m3
θx
25
day
Van/V
0.3
r
2
20Table 2.6: Membrane Operating Data
Parameter
Values
Unit
K
100
LMH/bar
J
25
LMH
tb
0.167
h
τb
0.013
h
Jb
35
LMH
n
938
∆Pm
0.25
bar
SADm
0.92
m3/(m2h)
tc
168
h
τc
2
h
cc
0.25
kg/m3
JCIP
45
LMH
21Table 2.7: Aeration Operating Data
Parameter
Biology
Membrane
Diffuser type
Fine bubble
Coarse bubble
Page | 40
OTE per m
0.05
0.02
α
-
0.49
β
-
0.95
Φ
-
0.89
Parameter
Values
Unit
V
2980
m3
Van
894
m3
Se
0.81
g/m3
Ne
0.018
g/m3
Ro
1395
Kg/day
Aerobic HRT(average)
14.3
h
Aerobic HRT(peak)
3
h
Anoxic HRT(average)
4.3
h
Anoxic HRT(peak)
0.9
h
R’ o
1434
N kg/day
Parameter
Values
Unit
NOx
40
g/m3
Px
654
kg/day
Xo
300
kg/day
Px + Xo
954
kg/day
QW
119
m3/day
QW/(J’netAm)
0.02
m3/m3
22Table 2.8: Biological Parameters
23Table 2.9: Sludge yield
Page | 41
24Table 2.10: Membrane calculations
Parameter
Values
Unit
Am
9887
m2
Area per element
250
m2
Actual membrane area
10000
m2
Number of elements
40
K’
120
N LMH/bar
Jnet
21
LMH
Jnet,actual
20
LMH
J’net,actual
25
N LMH
J’b
42
N LMH
J’actual
30
N LMH
Parameter
Values
Unit
Aeration Time
0.5
h/h
QA,m
4600
m3/h
Q’A,m
4729
Nm3/h
SADm
0.47
Nm3/(hm2)
SADp
19.2
Nm3/m3
MA,m
139110
kg/day
vc
225
kg
Mc
0.0065
kg/m3
25Table 2.11: Membrane Operation
26Table 2.12: Aeration Design
Parameter
Values
Unit
Tank depth
3
m
Pa,2
131
kPa
OTE membrane
0.06
%
Page | 42
OTE biological
0.14
%
Q’A,m
1.61
Nm3/s
O2 transferred by membrane aeration
24.87
kg/day
O2 required to maintain biology
1409
kg/day
Q’A,b
1.38
Nm3/s
27Table 2.13: Power Requirement
Air
blower Value
Unit
parameter
Liquid
pump Value
Unit
parameter
ξblower
0.50
Power(biological)
80.70
kW
Power(permeate) 3.44
kW
Wb
0.40
kWh/m3
Wh
0.02
kWh/m3
Power(membrane) 94.27
kW
Power(recycle)
9.11
kW
Wb,v
kWh/m3
Wp
0.04
kWh/m3
0.46
ξpump
0.45
A degree of caution is required in interpreting these data in that: a) The calculation does not account for the impact either of membrane life, which may possibly relate to permeability (which is generally higher for the FS modules), or sludge dry solids concentration on sludge disposal costs. b) There is considerable scatter in the data from which the Jnet:SADm correlations were obtained. Over the range of SADm values applied in practice for the same SADm value the operating cost of the HF module is _19% lower than that of the FS module. c) Many of the FS MBRs listed are operated without supplementary fine bubble aeration, such that the membrane aeration also provides air for bio treatment. This means that threes membranes may be over-aerated, which could also explain the higher permeabilities recorded compared with those of the HF MBRs. The one FS MBR operated with segregated membrane aeration yielded the lowest SADm value, the second lowest being that recorded for the doubledeck FS MBR
Page | 43
28Figure 2.1: Specific cost vs. flux for HS and FS technologies, flux to be related to aeration demand
29Figure 2.3: Specific cost vs. aeration demand over the ranges of aeration demand observed in practice for HF and FS technologies
Page | 44
2.3
Determination of Calculated Parameters
Pressure Calculations The net operating pressure (Pnet) for the RO systems was calculated according to the following equation: Pnet = [Pi - Po]/2 - Pp – Δπ = 0.25 bar
(1)
Where, Pnet = net operating pressure (Pa) Pi = pressure at the inlet of the pressure vessel (Pa) Po = pressure at the outlet of the pressure vessel (Pa) Pp = permeate pressure Δπ= net osmotic pressure of the feed and permeate (Pa)
The integrated averaging factor (IAF) assuming 100 percent salt rejection can be used to estimate the osmotic pressure as follows: Δπ = IAF x πf Where, πf = osmotic pressure of the feed stream (psi) IAF = 1.386 (for 50 percent recovery) Flow Calculations The net permeate rate for the MBR can be calculated using the equation:
QNET = (tON - tOFF / tON) x Qp = 23384
(2)
Where, QNET = net permeate rate (L/min) tON = the time the MBR membrane is in production (min) tOFF = the time the MBR membrane is in relaxation (min) Qp = Permeate flow rate (L/min) Please note: this calculation assumes the loss of flow during cleaning in place and intermittent maintenance cleans is negligible.
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Flux Calculation The flux of the MBR membranes can be calculated as follows: J = (Qp x 1440) / A = 25
(3)
Where, J = Membrane flux (L/day/m2) A = Total membrane surface area (m2) Temperature Correction Low-pressure membrane fluxes are normally temperature corrected to 20ºC, and RO membranes are corrected to 25ºC. The membrane fluxes for the MBR membranes can be temperature corrected with the following formula: J @ 20 ºC = J x e-0.0239(T-20) = 122
(4)
Where, T = feed water temperature (ºC) Specific Flux The specific flux is the relationship between flux and the net operating pressure. The relationship is defined by the formula: JSP = J/PNET = 21
(5)
Where, JSP = specific flux (LMD/Pa) Salt Rejection The salt rejection for the membranes was calculated using the following equation: R = 100 x (1 – Cp/ Cf) = 1395
(6)
Where, R = rejection (%) Cp = permeate conductivity (µΩ) Cf = feed conductivity (µΩ) Hydraulic Retention Time The hydraulic retention time (HRT) was calculated using the formula: HRT = V / (QNET x 60) = 14.5
(7)
Where, HRT = Hydraulic retention time (hours) V = MBR volume (L)
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Sludge Retention Time The sludge retention time (SRT) is defined as the total mass of activated sludge in the MBR divided by the mass flow rate of activated sludge being removed. In order to calculate the SRT of the MBRs, the reactors are treated as an ideal continuously stirred tank reactor (CSTR). Under this assumption, concentration of activated sludge in the MBR will be the same as the concentration in the waste stream and the equation will simplify as follows:
SRT = (VXR) / (QW XW) = V / QW = 25
(8)
Assuming that XR is equal to XW: Where, SRT = sludge retention time (days) XR = volatile suspended solids in the reactor (mg/L) XW = volatile suspended solids in the waste stream (mg/L) QW = waste stream flow rate (m3/day) Recycle Ratio The recycle ratio (RR) for MBR systems operating with anoxic and aerobic tanks is defined as the ratio of the flow of MLSS from the aerobic tank to the anoxic tank, divided by the net permeate rate. The RR of MBR is calculated as follows: RR = (QR-membrane - QNET) / QNET = (QR / QNET) – 1
(9)
Where, RR = Recycle Ratio 2.4
Sizing of the MBR
Packing density given by ratio of fibre surface area to volume Φ = Af / V
(1)
Where Af = surface area of fibres
= Nπdf
(2)
= Nπdf 2/4
(3)
V = module volume Av = volume occupied by fibres So: Av/ Af = df / 4
(4)
Thus: Ax = (4V – df Af) / 4L
(5)
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Where Ax = free x-sectional area
So: QA = 3600U / 4L x (4V - – df Af)
(6)
Where QA = aeration rate in m3/hr U = air flow velocity in channels (m/s) SADm = 3600U / 4V x (4V/Af – df)
(7)
Where SADm = aeration demand with respect to fibre area Substituting for V/Af and normalizing against flux: SADp = 3.6x106U / 4LJ x (4/ Φ – df)
(8)
Where SADp = aeration demand with respect to permeate volume Evidence suggests that J is a linear function of aeration intensity: J = mU + c
(9)
Where m and c are empirical constants So: SADp = 3.6x106U / 4L (mU + c) x (4/ Φ – df)
(10)
Aeration energy demand in kWh/m3 permeate is then given by EA = 0.0303 SADp γ x [((10x + 101) / 101)(1 – 1/ γ) – 1] / (γ – 1) ζ (11) Where γ = aerator constant = 1.4 ζ = blower efficiency = 0.5 x = aerator depth = 3 m So: EA = Uk / L (mU + c) x (4/ Φ – df)
(12)
Where K = 0.0303 x 3.6x106 / 4 x γ x [((10x + 101) / 101) (1 – 1/
γ)
– 1] / (γ – 1) ζ and is thus
constant for a given system. Now, commercial technical data for available membrane modules (Judd, 2006) suggests that, for packing density and fiber diameter respectively in m-1 and m: 1 / Φ ≈ gdf + 0.001 f
(13)
Where f = 0.7-1.7 and g = 0.9-1.1 Thus
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EA = Uk / L (mU + c) x [(4/g-1) df + 0.004f)
(14)
For the four main MBR HF membrane suppliers, g = 0.89 (R2 = 0.97) and f = 1.7, and thus:
EA = Uk / L (mU + c) x [3.5 df + 0.0068]
2.5
(15)
Summary
The selection of appropriate design and operating parameter values for an iMBR centers on: choice of membrane module; choice of membrane aerator, if the membrane module is not provided with an integral aerator; Membrane aeration rate. Many, if not all, of these facets are stipulated by the technology provider, and the choice of technology itself (including that between iMBR and sMBR) will be strongly influenced by the duty to which it is being put. However, broadly speaking the mean permeability sustained in an iMBR is dependent on the aeration rate. Failure of membrane surface fouling, which can be irrecoverable, and clogging of the membrane channels. It is therefore essential that the maintenance schedule includes cleaning of the aerators, normally achieved by flushing with a water or hypochlorite solution. Design of iMBRs relies on accurate information regarding oxygen transfer to the biomass and maintenance of permeability by membrane aeration. The design proceeds via calculation of the oxygen demand of the biomass, which relates primarily to the feed water composition, the solids retention time and the oxygen transfer efficiency. This procedure applies to all bio treatment processes. However, for an MBR complications arise when estimating the oxygen transfer and hydraulic performance (flux and permeability) provided by the membrane aeration. The correlation of membrane flux and permeability with membrane aeration rate and the applied cleaning protocol relies entirely on heuristically-derived information. Minor: Oil-Water Separator
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2.6
Oil-Water separator design
Oil-water separation theory is based on the rise rate of the oil globules (vertical velocity) and its relationship to the surface-loading rate of the separator. The rise rate is the velocity at which oil particles move toward the separator surface as a result of the differential density of the oil and the aqueous phase of the wastewater. The surface-loading rate is ratio of the flow rate to the separator to the surface area of the separator. The required surface-loading rate for removal of a specified size of oil droplet can be determined from the equation for rise rate. The following parameters are required for the design of an oil-water separator: a) Design flow (Qm), the maximum wastewater flow. The design flow should include allowance for plant expansion and storm water runoff, if applicable. b) Wastewater temperature. Lower temperatures are used for conservative design. c) Wastewater specific gravity (Sw). d) Wastewater absolute (dynamic) viscosity (µ). Note: Kinematic viscosity (v) of a fluid of density (ρ) is v = µ /ρ. e) Wastewater oil-fraction specific gravity (So). Higher values are used for conservative design. f) Globule size to be removed. The nominal size is 0.015 centimeters (150 micrometers), although other values can be used if indicated by specific data.
The design of conventional separators is subject to the following constraints: a) Horizontal velocity (vH) through the separator should be less than or equal to 1.5 cm/s (0.015 m/s) or equal to 15 times the rise rate of the oil globules (Vt), whichever is smaller. b) Separator water depth (d) should not be less than 1 m, to minimise turbulence caused by oil/sludge flight scrapers and high flows. Additional depth may be necessary for installations equipped with flight scrapers. It is usually not common practice to exceed a water depth of 2.4 m. c) The ratio of separator depth to separator width (d/B) typically ranges from 0.3 to 0.5 in refinery services.
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d) Separator width (B) is typically between 1.8 and 6 m in refinery services. e) By providing two separator channels, one channel is available for use when it becomes necessary to remove the other from service for repair or cleaning. f) The amount of freeboard specified should be based on consideration of the type of cover to be installed and the maximum hydraulic surge used for design. g) A length-to-width ratio (L/B) of at least 5 is suggested to provide more uniform flow distribution and to minimize the effects of inlet and outlet turbulence on the main separator channel.
30Figure 2.4: Design variables for oil interceptors.
The oil-globule rise rate (Vt) can be calculated by Equation 1 or 2 shown below. Equation (1) should be used when the target diameter of the oil globules to be
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removed is known to be other than 0.015 cm and represents a typical design approach. Equation (2) assumes an oil globule size of 0.015 cm. Vt = g/18µ(ρw – ρo)D2 Vt = 0.0123[(Sw – So)/µ, (Where D = 0.015cm) Where: Vt = vertical velocity, or rise rate, of the designed oil globule, in cm/s. g = acceleration due to gravity (981 cm/s2) µ = absolute viscosity of wastewater at the design temperature, in poise ρw = density of water at the design temperature, in g/cm3 ρo = density of oil at the design temperature, in g/cm3 D = diameter of oil globule to be removed, in cm Sw = specific gravity of the wastewater at the design temperature (dimensionless) So = specific gravity of the oil present in the wastewater (dimensionless) Alternatively, if using kinematic viscosity equations 1 and 2 may be rearraged as follows: Vt = g/18v(1-So)D2 Vt = 0.0123(1-So/v) Where, V = kinematic viscosity of the wastewater at the design tempearature,in stokes. Horizontal Velocity (vH) The design mean horizontal velocity is defined by the smaller of the values for vH in cm/s obtained from the following two constraints:
Minimum Vertical Cross-Sectional Area (Ac) Using the design flow to the separator (Qm) and the selected value for horizontal velocity (vH), the minimum total cross-sectional area of the separator (Ac) can be determined from the following equation: Ac = Qm x 100/ VH Where: Ac = minimum vertical Cross- sectional area, in m2 Qm = design flow to the separator, in m3/s VH = horizontal velocity, in cm/s
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Channel Width and Depth Given the total cross-sectional area of the channels (Ac) and the number of channels desired (n), the width and depth of each channel can be determined. A channel width (B), generally between 1.8 - 6 m, should be substituted into the following equation, solving for depth (d): d = Ac/Bn Where: d = depth of channel, in m B = width of channel, in m Separator Length Once the separator depth and width have been determined, the final dimension, the channel length (L), is found using the following equation: L = F(VH/Vt)d Where: L = length of channel, in m F = turbulence and short-circulated factor (dimensionless) VH = horizontal velocity, in cm/s D = depth of channel, in m If necessary, the separator’s length should be adjusted to be at least five times its width, to minimize the disturbing effects of the inlet and outlet zones. Equation is derived from several basic separator relations: a) The equation for horizontal velocity (vH = Qm/Ac/), where Ac is the minimum total cross-sectional area of the separator. b) The equation for surface-loading rate (Vt = Qm/AH), where AH is the minimum total surface area of the separator. c) Two geometrical relations for separator surface and cross-section area (AH = LBn and Ac= dBn), where n is the number of separator channels. The turbulence and short-circuiting factor (F) is a composite of an experimentally determined short-cutting factor of 1.21 and a turbulence factor whose value depends on the ratio of mean horizontal velocity (vH) to the rise rate of the oil globules (Vt). A
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graph of F versus the ratio vH/Vt is given in Figure1.5; the data used to generate the graph are also given below. 31Figure 2.5: Recommended values of F for various values of Vh/Vt
Minimum Horizontal Area In an ideal separator - one in which there is no short-circuiting, turbulence, or eddies – the removal of a given suspension is a function of the overflow rate, that is, the flow rate divided by the surface area. The overflow rate has the dimensions of velocity. In an ideal separator, any oil globule whose rise rate is greater than or equal to the overflow rate will be removed. This means that any particle whose rise rate is greater than or equal to the water depth divided by the retention time will reach the surface, even if it starts from the bottom of the chamber. When the rise rate is equal to the overflow rate, this relationship is expressed as follows:
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Vt = di/Ti = 100di/(LiBidi/Qm) = 100Qm/LiBi = Vo Where: di = depth of wastewater in an ideal separator, in cm Ti = retention time in an separator, in s Li = length of an ideal separator, in cm Bi = width of an ideal separator, in cm Qm = design flow to the separator, in m3/s Vo = overflow rate, in cm/s
The equation establishes that the surface area required for an ideal separator is equal to the flow of wastewater divided by the rise rate of the oil globules, regardless of any given or assigned depth. By taking into account the design factor (F), the minimum horizontal area (AH), is obtained as follows: AH = F(Qm x 100/Vt) Where: AH = minimum horizontal area, in m2 F = turbulence and short-circuit factor Qm = design flow to the separator, in m3/s Vt = vertical velocity, or rise rate, of the designed oil globule, in cm/s. Qm/AH = 0.00196(Sw – So)/µ Maintenance Parallel-plate units may experience clogging problems if the plate inclination is too shallow or the plate-to-plate spacing is too narrow. It has also been reported that sand entering the plate system can collect at the entrance to the plate assembly and reduce flow through the lower plate sections. Should blockages develop, they may be cleared by removing the accumulated solids, flushing the plate pack with water or air, or mechanical cleaning. Operating and maintenance manuals and equipment suppliers should be consulted with regard to approved procedures. Solids accumulation and clogging should be considered before installation and designed for accordingly.
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Parallel-plate packs do not generally clog if they are properly designed, installed, and maintained. If significant solids levels are expected, the plate inclination should be about 60o, which exceeds the angle of repose of practically all solids encountered in such systems. A plate slope of 60o and periodic blowdown of accumulated solids should help to avoid most parallel-plate separator plugging problems. Construction Details A variety of parallel-plate equipment configurations are commercially available. In the case of conventional separators retrofitted with parallel plates few, if any, additional fitments are required in addition to those already present. New parallelplate separators have a wide range of design features and may be purchased as packaged units, with oil and sludge-draw off equipment provided. Consequently, specific construction and fitment details are omitted from this subsection. Two major types of parallel-plate separators are marketed: the cross-flow inclined plate and the down-flow inclined plate. Cross-flow separators that employ parallel plates oriented vertically and horizontally are also available, although there are few applications for them in wastewater treatments. In a cross-flow separator, shown in sketch bellow, flow enters the plate section from the side and flows horizontally between the plates. Oil and sludge accumulate on the plate surfaces above and below the wastewater flowing between the plates. As the oil and sludge build up, the oil globules rise to the separator surface and sludge gravitates toward the separator bottom. In a down-flow separator, the wastewater flows down between the parallel plates, sludge deposited on the lower plates flows to the bottom of the separator, and oil accumulated beneath the upper plate flows counter-current to the waste flow to the top of the separator.
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32Figure 2.6: sketch of Parallel plate separator - cross-flow
[Courtesy of Sepa Waste Water Treatment Pty. Ltd., Australia] Terminal Velocity of Oil Globules in Water The basic principles of separation by gravity differential can be expressed mathematically and applied quantitatively. When a particle is allowed to move freely in a fluid and is subjected to gravitational force, its rising or settling velocity with respect to the fluid becomes a constant when the resistance to motion equals the weight of the particle in the fluid. In other words, the resistance to motion of a particle in a liquid medium is equal to the effective weight of the particle when the terminal velocity has been reached, namely, when the acceleration caused by gravity becomes zero. The general equation for this resistance, first proposed by Newton, is as follows: Df = CA(ρwV2/2) Where: Df = Particle’s resistance to motion in liquid medium, in dynes C = Coefficient of drag A = projected area of oil globules, in cm2 ρw = density of water, in g/cm3 V = terminal velocity of oil globule in water, in cm/s The equation for the effective weight of the particle is as follows:
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W = ( D3/6) x ( ρw – ρo)g Where: W = effective weight of the oil globule in water, in dynes D = diameter of oil globule, in cm ρo = density of the oil globule, in g/cm3 g = acceleration caused by the force of gravity (981 cm/s2) Equating equations above: CA(ρwV2/2) = (πD3/6) x ( ρw – ρo)g Given that, for a sphere, A = D2/4 Then the rate of rise is as follows:
The equation for the resistance to motion of a small spherical particle at its terminal velocity is as follows:
Where: µ = absolute viscosity of wastewater the design temperature, in poises If W in Equation above is equated to Df in Equation 16, a new expression for V is obtained. By the substitution of Vt, the oil globules’ velocity of rise (in cm/s) for the general term V, the well-known form of Stokes’ law for the terminal velocity of spheres in a liquid medium becomes applicable to the rate of rise of oil globules in water. Equations should theoretically include a deformation coefficient that depends on the relative viscosities of the oil and the water; however, in practice, the coefficient is not required to estimate the rate of rise of small oil globules in wastewater.
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Where: Cv = deformation coefficient theoretically applicable µ1 = absolute viscosity of the particle, in poises µ2 = absolute viscosity of the medium, in poises If this correction for internal flow is applied to Equation 17, Stokes’ law for determining the rate of rise of an oil particle in water would become the following:
Equations above are strictly correct only when the rising particle’s Reynolds number (based on the particle diameter) is less than 0.5. For the range of Reynolds numbers resulting from the computations in this chapter (all substantially less than unity), however, the deviation from Stokes’ law is negligible for design purposes. Size and Gravity of Oil Globules From the results of experiments and from plant operating data, it has been determined that the design of wastewater separators should be based on the rise rate of oil globules with a diameter of 0.015 cm (150 micrometers). To check the dimensions of this formula, it is necessary to note that the number 0.0123 was obtained from dimensional factors and therefore has the dimensions of its factors, which are as follows:
If the globule diameter is 60 micrometers (i.e., D = 0.006), the factor is 0.0020, rather than 0.0123. Derivation of Equation for Separator Length Separator length is calculated from the following equation: L = F(vH/vt)d
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The basis equations used to derive the equation for separator length are AH = FQm/vt ; Ac = Qm/ vH; Ac = dBn Therefore; L = AH/Bn = AH/(Ac/d) = AHd/Ac = [(FQm/ vt) x d] / (Qm/ vH) L = L = F(vH / vt)d Where: AH = total separator surface area L = length of separator channel B = widthof separator channel N = number of separator channels F = turbulence and short-circuiting factor Qm = total design flow to separator Ac = separator’s total cross sectional area vH = separator’s horizontal velocity vt = separators surface-loading rate d = depth of separator channel Calculation and results Data Given:
Sewage Flow = 70000 m3/day = 0.8102 m3/s
Temperature = 29 °C
Assumptions taken:
Specific gravity of water = 0.99
Specific gravity of oil = 0.92
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Viscosity of wastewater = 0.0062 poise = 0.3871 cm2/s
Oil globule size = 0.015 cm
Design constraints •
VH ≤ 1.5 cm/s or VH = 15 Vt, whichever the smaller
•
1.0 m ≤ d ≤ 2.5 m
•
0.3 ≤ d/B ≤ 0.5
•
1.8 m ≤ B ≤ 6.0 m
•
n = 2 (minimum 2 channels)
•
L/B ≥ 5
Calculating Vt using: Vt = 0.0123[(Sw - So)/μ] Vt = 0.0123[(990 – 920)/ (0.3871)] Vt = 2.224 cm/s Vertical Velocity = 2.224 cm/s Horizontal flow velocity is taken as 1.5 cm/s Ac = (0.8102 x 100)/1.5 Ac = 54 m2 Therefore the minimum vertical cross-sectional area is 54 m2 Similarly, By assuming ‘B’ to be 8m and n = 2 d = 54/ (8 x 2) d =3.38 m Depth of channel = 3.38 m
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Depth/width ratio = 3.38/8 = 0.4 Calculating L using: Using the following graph:
F is found to be 1.46 Hence, L = F x (VH/Vt) x d L = 1.46 x (1.5/2.224) x 3.38 L = 1.46 x 0.67446 x 3.38 L = 3.33 m Length of channel = 3.33 m
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Design inputs: Sewage Flow (in m3/s)
0.8102
Temperature (in °C)
29
Specific gravity of water
0.99
Specific gravity of oil
0.92
Viscosity of wastewater (in poise)
0.0062
Oil globule size (in cm)
0.015
Results: Vertical Velocity (in cm/s)
0.18083
Horizontal flow velocity ( in cm/s)
1.5
minimum vertical cross-sectional area (in m2)
54
number of channels
2
Width of channel (in m)
8
Depth of channel (in m)
3.38
Length of channel (in m)
3.33
2.7
PIPE SELECTION AND PIPE SIZING FOR MBR TANKS OUTLETS AND INLETS
Pipe Selection When it comes to pipes for transportation of liquids, we are exposed to a variety of the pipes which normally are made of plastic, concrete or metal (e.g. galvanized iron or copper and stainless stain) to make our choices. However, if we consider the cost of copper for the transportation of effluent of a treatment plant, it is definitely not feasible. Similarly while opting for a particular pipe material for transportation of liquids the key factors that need to be considered are: water characteristics and chemistry and resistant against a specified internal and external pressure. Thus to start with the primary factor is the water chemistry and characteristics which include pH, salts that are dissolved in the water and among other. Likewise it is be noted that there would be an alteration in the initial pH of the effluent since the latter has been
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subjected to a coagulation and flocculation process with help of alum which has the tendency to render the effluent to be slightly more acidic: pH changes from 6.5 to approximately 4.7 (Tchobanoglous, et al., 2004). Subsequently we can expect the corrosiveness of the effluent to material to increase; thus the prime requirement for the pipe material would be higher corrosion resistance. Hereby the choice of metal as pipe material can be crossed from the initial list; therefore the best suited pipe material for the MBR is plastic. The raw material needed to make most plastic comes from petroleum and natural gas. Due to their relatively low costs, ease in manufacture, versatility and imperviousness to water, plastics are used in an enormous and expanding range of products: from paper clips to pipes intended for transporting drinking water. Plastic has replaced many common materials such as cement and metals within drinking water networks (WECF, 2012). Plastics are often preferred than metals due to a number of intrinsic advantages: plastic piping is lightweight and does not require an open flame for joining the flexibility of plastic can simplify the installation. Plastics are typically lower in cost and resist the corrosion and scaling that plague metals in some applications. However, indication of the mitigation of synthetic chemical contaminants from plastic pipe materials to water may exist. These contaminants likely occur at low “safe levels”, but are sufficient to generate odor and taste concerns in some cases. Another disadvantage of some types of plastic pipes is that they have lowered resistance to chlorinated water; which will be not problematic in our case. Likewise the most common types of plastic used in water and wastewater applications are PE (Polyethylene) pipes and PVC (Polyvinyl chloride) pipes (WECF, 2012)... PE (Polyethylene) pipes There are basically three of PE (Polyethylene) pipes: high-density polyethylene (HDPE), medium density (MDPE) and low density (LDPE) pipes. The level of density expresses the pressure that the pipes can sustain. For locations enduring high pressure or weight, like streets, HPPE pipes are used. Performances of PE pipes of different manufactures show different possible temperature ranges in terms of application and usually range between -20 and + 900C. PE pipes are widely used for water and
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sanitation systems. High-quality PE pipes have a long lifetime (50 years) and are easy to maintain. They have high impact strength and show resistance to cracking even at low temperatures. PE pipes are also stable in water and do not tend to corrode (WECF, 2012). PVC (Polyvinyl chloride) pipes PVC is the third most widely produced plastic after PE and PP (polypropylene). PVC is widely used in construction because it is cheap, durable and easily workable but nevertheless the material tends to get brittle in the long- term. Simultaneously from an environmental point of view the usage of PVC is controversial, particularly because of the harmful chemicals (e.g. dioxins) which may be released in the environment during its production and final disposal (burning) (WECF, 2012).. Finally it can be concluded that a medium density polyethylene (MDPE) pipe is best suitable for the Membrane biological reactor tank: due to the versatility of being corrosion resistance and also sustain pressure to which it would be exposed to. In addition its low cost relative to other pipe material like copper and extended lifetime render it to be more attractive. Pipe sizing There are basically two methods reported by Sinnott, 2005 through which we can proceed to evaluate the optimum diameter of a pipe: either using economic pipe diameter formula or Simpson correlation (1968). However due to lack of information related to economic pipe diameter for medium density polyethylene we will go by Simpson correlation. Simpson (1968) gives values for the optimum velocity in terms of the fluid density. His values, converted to SI units and rounded, are:
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33Table 2.14: Fluid density and Velocity
Similarly together with the Simpson correlation we shall abide by the following assumptions for the evaluating of the optimum diameter. a) The piping system should be designed for the maximum flow-rate output from the MBR tank that is 50000 m3/hr. However to increase the reliability and not to oversize the pump and piping system; we will assume that delivery of 3125 m3 of effluent will be performed by three pumps and we have one additional stand by pump for any contingency. b) Usually we can expect the temperature of the effluent to experience a drop. likewise the temperature drop will somehow be dependent on the season prevailing in the country, however since we lack data to evaluate any raise or drop we will simply assume that the temperature of the effluent remain at 25℃. c) The density of the effluent is similar to that water at 250C: 997.048kg/m3; the ideology behind this assumption is that the effluent before entering the MBR is subjected to several pre-treatment namely: oil and grease removal, grit removal and coagulation and flocculation process which will enable the removal of several contaminants which otherwise might influence its density at 250C. d) The viscosity of effluent is again similar to that of water at 25 0C: 0.890 x 10-3 Ns/m2 and the same ideology as density applies for viscosity. Calculations If we consult the fluid density and optimum velocity table by Simpson is can be noted that we do not have any specific optimum velocity value for a fluid density of
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997.048kg/m3; thus by graphical interpolation of the data was performed to estimate the optimum velocity of the fluid and found to be 2.7 m/s.
Consequently the internal diameter of the pipes for MBR is evaluated to be 40 cm. 2.8
Pump selection for MBR
Pumps are generally classified in two classes: 1. Dynamic pumps, such as centrifugal pumps. 2. Positive displacement pumps, such as reciprocating and diaphragm pumps. Pump selection is made on the flow rate and head required, together with other process considerations, such as corrosion or the presence of solids in the fluid. Table 2.15 provides a brief description and application of many types of pumps in these two classes. 34Table 2.15: Pump Types and Major Applications in Wastewater treatment
Major Classification
Pump Type
Major Pumping Application Raw water and wastewater,
Centrifugal
secondary sludge return and wasting, settled primary and thickened sludge, effluent
Kinetic Peripheral Rotary
Scum. grit, sludge and raw water and wastewater Lubricating oils, gas engines,
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chemical solutions, small flows of water and wastewater Scum and primary, secondary, Plunger
and settled sludge; chemical solution Secondary
Airlift
sludge
circulation
and wasting, grit
Positive Displacement Pneumatic ejector
Raw wastewater at small installation (100 to 600 L/min) Grit, settled primary and
Screw
secondary sludge, thickened sludge, raw wastewater
Diaphragm
Chemical solution
Source: (Spellman, 2003) Considering the data obtained from table above it can be said that the best suited pump for pumping effluent from the MBR is the centrifugal pump. In addition the centrifugal pump is by far the most widely used type in the chemical and petroleum industries. Furthermore with its ability to pump liquids with very wide-ranging properties and suspensions with a high solid content including, for example, cement slurries, and clearly demonstrate the superiority among of the latter other pumps in wastewater applications. Likewise it may be constructed from a very wide range of corrosion resistant materials. The whole pump casing may be constructed from plastics such as polypropylene or it may be fitted with a corrosion resistant lining. Because it operates at high speed, it may be directly coupled to an electric motor and it will also give a high flow-rate for its size (Sinnott, 2005). 2.9
Power requirements for pumps in MBR
To transport a liquid from one vessel to another through a pipeline energy has to be supplied to: 1. Overcome the friction losses in the pipes;
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2. Overcome the miscellaneous losses in the pipe fittings (e.g. bends), values, instruments, etc. 3. Overcome the losses in process equipment (e.g. primary clarifier); 4. Overcome any difference in elevation from end to end of the pipe; 5. Overcome any difference in pressure between the vessels at each of the pipeline. Hence the total energy required can be calculated from the equation: g∆z + ∆P/ρ - ∆Pf/ρ – W = 0 Where: W = work done, J/kg ∆z = difference in elevation (z1 – z2), m ∆P = difference in system pressure (P1 – P2), N/m2 ∆Pf = pressure drop due to friction, including miscellaneous losses, N/m2 ρ = Liquid density, kg/m3 g =acceleration due to gravity, m/s2 Similarly the head required from the pump = ∆P/ρg - ∆Pf/ρg - ∆z Total head required will be the sum of the dynamic head due to friction losses in the piping, fittings, valves and process equipment, and any static head due to differences in elevation. Pressure drop in pipelines The pressure drop in a pipe, due to friction, is a function of the fluid flow-rate, fluid density and viscosity, pipe diameter, pipe surface roughness and the length of the pipe. It can be calculated using the following equation: ∆Pf = 8f(L/di)ρu2/2 Where: ∆Pf = pressure drop, N/m2
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F = friction factor L = pipe length, m di = pipe inside diameter, m ρ = fluid density, kg/m3 u = fluid velocity, m/s The friction factor is a dependent on the Reynolds number and pipe roughness. The friction factor for use in equation 2.8.1 can be found from Figure 2.7
Where:
Relative roughness, e = absolute roughness/pipe inside diameter Note: the friction factor used in equation 5.3 is related to the shear stress at the pipe wall, R, by the equation:
Miscellaneous pressure losses In addition to pressure loss in pipelines, any obstruction to flow will generate turbulence and cause a pressure drop. So, pipe fittings, such as: bends, elbows, reducing or enlargement sections, and tee junctions, will increase the pressure drop in a pipeline. There will also be a pressure drop due to the valves used to isolate equipment and control the fluid flow. The pressure drop due to these miscellaneous losses can be estimated using either of two methods: 1. As the number of velocity heads, K, lost at each fitting or valve. A velocity head is u2/2g, meters of the fluid, equivalent to (u2/2) ρ, N/m2. The total number of
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velocity heads lost due to all the fittings and valves is added to the pressure drop due to pipe friction (Sinnott, 2005). 2. As a length of pipe that would cause the same pressure loss as the fitting or valve. As this will be a function of the pipe diameter, it is expressed as the number of equivalent pipe diameters. The length of pipe to add to the actual pipe length is found by multiplying the total number of equivalent pipe diameters by the diameter of the pipe being used (Sinnott, 2005). The number of velocity heads lost, or equivalent pipe diameter, is a characteristic of the particular fitting or type of valve used. Values can be found in handbooks and manufacturers’ literature. Summary of results With help of the literature review above the calculations were performed and the main results have been tabulated below. 35Table 2.17: Summary of result involving the main pipeline connecting the MBR
Pipeline description
Pipeline between primary Output pipeline of MBR clarifier to MBR tank
Pipeline length Optimum
flow-rate
26 m of 5000 m3/hr
33 m 5000 m3/hr
effluent Optimum Pipe Diameter
40 cm
40 cm
Reynolds number
1.03×106
1.3×106
Friction factor
0.0065
0.0065
Miscellaneous losses in
284 m
86 m
Pressure drop in pipeline
95.52 kPa
108.12 kPa
Effective pressure drop in
280.52 kPa
108.12 kPa
Power requirement
149.04 J/kg
137.81 J/kg
Head required
15.19 m
3.63 m
equivalent pipe diameter
pipeline
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CHAPTER 3: Heat and material Balance 3.1
Material Balance for the MBR
I.
Mass Balance on the MBR
Influent = Waste Sludge + Effluent
Q = Influent Flowrate
SE = BOD in Effluent, 𝑚𝑔⁄𝐿
S0 = BOD in influent, 𝑚𝑔⁄𝐿
Hence BOD efficiency can be calculated as follows: Given: BOD in domestic wastewater entering Primary Settling Tank = 307 𝑚𝑔⁄𝐿 Assuming BOD removal efficiency in primary clarifier = 40 % Primary effluent BOD = 307 𝑚𝑔⁄𝐿 × (1 − 0.40) = 184 𝑚𝑔⁄𝐿 Therefore; As assumed permissible limits, that is 40 mg/L = 2800 kg/day is in the effluent BOD Removal Efficiency in MBR =
184 𝑚𝑔⁄𝐿 −40𝑚𝑔⁄𝐿 184𝑚𝑔⁄𝐿
× 100 = 78%
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307 𝑚𝑔⁄𝐿 −40𝑚𝑔⁄𝐿 )× 307𝑚𝑔⁄𝐿
Hence; 𝑂𝑣𝑒𝑟𝑎𝑙𝑙 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 = (
100 = 87%
The recycle ratio can be expressed as follows: 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝐹𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑚3 ⁄𝑑𝑎𝑦 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝑅𝑎𝑡𝑖𝑜 = 𝐼𝑛𝑓𝑙𝑢𝑒𝑛𝑡 𝐹𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑚3 ⁄𝑑𝑎𝑦 Typical recycle ratio for conventional activated sludge process = 0.25 – 0.50 Average Recycle Ratio = 0.375 Therefore; 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝐹𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑄𝑅 = 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝑟𝑎𝑡𝑖𝑜 × 𝐼𝑛𝑓𝑙𝑢𝑒𝑛𝑡 𝑓𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑄0 = 0.375 × 70000 𝑚3 ⁄𝑑𝑎𝑦 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝐹𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑄𝑅 = 26250 𝑚3 ⁄𝑑𝑎𝑦 Also by the methodology of Shu Dar lin (2005), 𝑄𝑅 can be expresses as follows: 𝑄𝑅 =
𝑄0 (𝑥 − 𝑥0 ) 𝑥𝑤 − 𝑥
Whereby: X = MLSS concentration, 2500 𝑚𝑔⁄𝐿 X0 = Primary Effluent TSS, 102.6 𝑚𝑔⁄𝐿 𝑄𝑅 = 𝑟𝑒𝑐𝑦𝑐𝑙𝑒 𝑓𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 26250 𝑚3 ⁄𝑑𝑎𝑦 26250 𝑚3 ⁄𝑑𝑎𝑦 =
70000 𝑚3 ⁄𝑑𝑎𝑦 (2500 𝑔⁄𝑚3 − 102.6 𝑔⁄𝑚3 ) 𝑥𝑤 − 2500 𝑔⁄𝑚3 𝑥𝑤 = 3893.07 𝑔⁄𝑚3
Also; 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝑅𝑎𝑡𝑖𝑜 =
𝑄𝑅 𝑋 = 𝑄0 𝑋𝑅 − 𝑋
Whereby: 𝑋𝑅 is the concentration in recycle sludge and as assumed R is 0.375.
Page | 73
2500 𝑔⁄𝑚3 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝑅𝑎𝑡𝑖𝑜 = 𝑋𝑅 − 2500 𝑔⁄𝑚3
Inlet Flowrate:XO = Concentration of TSS in influent Primary Settling Tank Outlet Flowrate:Xe = Concentration of Biomass in effluent Return Sludge: QR = return flow pumping rate, 𝑚3 ⁄𝑑𝑎𝑦 Xu = return microorganism concentration Waste Activated Sludge: QW = Waste flow from recycle waste line, 𝑚3 ⁄𝑑𝑎𝑦 And µ = growth of solids (𝑑𝑎𝑦 −1 )
II.
BOD Balance around MBR
𝐼𝑛𝑝𝑢𝑡 − 𝑜𝑢𝑡𝑝𝑢𝑡 + 𝑔𝑒𝑛𝑒𝑟𝑎𝑡𝑖𝑜𝑛 = 𝑎𝑐𝑐𝑢𝑚𝑢𝑙𝑎𝑡𝑖𝑜𝑛 (𝑄0 𝑆0 + 𝑄𝑅 𝑆𝐸 ) − (𝑄0 + 𝑄𝑅 )𝑆𝐸 −
𝜇𝑋𝑉 𝑑𝑆 = 𝑉 𝑌 𝑑𝑡
𝑑𝑆 𝑉=0 𝑑𝑡 Y = cell yield in kg MLSS/ kg BOD removed At steady state 𝜇𝑋𝑉 = 𝑄0 𝑆0 − 𝑄0 𝑆𝐸 𝑌 𝜇 𝑄0 (𝑆0 − 𝑆𝐸 ) = 𝑓⁄𝑚 𝑟𝑎𝑡𝑖𝑜 = 𝑌 𝑉𝑥 𝑆0 = 184 𝑚𝑔⁄𝐿 Assuming no chemical changes occur: 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝐵𝑂𝐷𝐸 = 40 𝑚𝑔⁄𝐿 Therefore:
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𝐵𝑂𝐷𝑅 = 𝐵𝑂𝐷𝑊𝐴𝑆 = 40 𝑚𝑔⁄𝐿 III.
Flow Balance
Influent Flow Q0 = 70,000 m3/day Initial BOD = BOD0 = 184 g/m3 As calculated: BOD Efficiency = 78 % BOD in Effluent = 40 g/m3 IV.
Solid Balance on membrane
𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑇𝑆𝑆 𝑖𝑛 𝑅𝐴𝑆 = 𝑇𝑆𝑆𝑅 = 𝑋𝑈 𝑔⁄𝑚3 × 𝑄𝑅 𝑚3 ⁄𝑑𝑎𝑦 𝑇𝑆𝑆𝑅 = 10.65 𝑘𝑔⁄𝑚3 × 26250 𝑚3 ⁄𝑑𝑎𝑦 = 279,562.5 𝐾𝑔⁄𝑑𝑎𝑦 𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑇𝑆𝑆 𝑖𝑛 𝑊𝐴𝑆 = 𝑋𝑢 𝑘𝑔⁄𝑚3 × 𝑄𝑊 𝑚3 ⁄𝑑𝑎𝑦 = 2367.07 𝑘𝑔⁄𝑑𝑎𝑦 Assume TSS Removal Efficiency = 81% Therefore: 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑂𝑓 𝑇𝑆𝑆 𝑖𝑛 𝐸𝑓𝑓𝑙𝑢𝑒𝑛𝑡 = 0.19 × 102.6 𝑚𝑔⁄𝐿 = 19.494 𝑚𝑔⁄𝐿 = 1364.6 𝑘𝑔⁄𝑑𝑎𝑦 V.
Balance on VSS on membrane
The removal efficiency of VSS in an MBR system is 90%, therefore; 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑟𝑖𝑜𝑛 𝑜𝑓 𝑉𝑆𝑆 𝑖𝑛 𝐸𝑓𝑓𝑙𝑢𝑒𝑛𝑡 = 10% × 82.08 𝑔⁄𝑚3 = 8.208 𝑔⁄𝑚3 = 574.6𝑘𝑔⁄𝑑𝑎𝑦 Whereby VSS = 80% TSS = 82.08𝑔⁄𝑚3 = 5745.6𝑘𝑔⁄𝑑𝑎𝑦 Assuming: 𝑉𝑆𝑆𝑊𝐴𝑆 = 𝑉𝑆𝑆𝑅 = 5745.6 𝐾𝑔⁄𝑑𝑎𝑦 − 574.6 𝐾𝑔⁄𝑑𝑎𝑦 = 5171.04 𝑘𝑔⁄𝑑𝑟𝑦 VI.
NH3-N Balance on the membrane skid
Overall Balance:
Page | 75
𝑁𝐻3 − 𝑁𝑖𝑛 = 𝑁𝐻3 − 𝑁𝑜𝑢𝑡 𝑁𝐻3 − 𝑁𝑂𝑈𝑇 = 𝑁𝐻3 − 𝑁𝐸 + 𝑁𝐻3 − 𝑁𝑊𝐴𝑆 By the methodology of N.F.Gray, 2005, the removal efficiency of 𝑁𝐻3 − 𝑁 in an ASP system is 90% 𝑁𝐻3 − 𝑁𝑖𝑛 = 1400 𝐾𝑔⁄𝑑𝑎𝑦 𝑁𝐻3 − 𝑁 𝑟𝑒𝑚𝑜𝑣𝑒𝑑 𝑖𝑛 𝑎𝑒𝑟𝑎𝑡𝑒𝑑 𝑡𝑎𝑛𝑘 = 90% × 1400 𝐾𝑔⁄𝑑𝑎𝑦 = 1260 𝑘𝑔⁄𝑑𝑎𝑦 𝑁𝐻3 − 𝑁𝐸 = 𝑁𝐻3 − 𝑁𝑊𝐴𝑆 = 𝑁𝐻3 − 𝑁𝑅 = 1400 𝐾𝑔⁄𝑑𝑎𝑦 − 1260 𝐾𝑔⁄𝑑𝑎𝑦 = 140 𝑘𝑔⁄𝑑𝑎𝑦 VII.
NO3-N Balance on membrane skid
Overall Balance: 𝑁𝑂3 − 𝑁𝑖𝑛 = 𝑁𝑂3 − 𝑁𝑜𝑢𝑡 Since nitrification occurs, let 𝑁𝑂3 − 𝑁𝑥 be the amount of nitrates obtained by the nitrification of ammonia. Therefore: 𝑁𝑂3 − 𝑁𝑖𝑛 = 𝑁𝑂3 − 𝑁1 + 𝑁𝑂3 − 𝑁𝑥 Assuming 𝑁𝑂3 − 𝑁𝑥 = 5031.2 Kg⁄day 𝑁𝑂3 − 𝑁𝑜𝑢𝑡 = 𝑁𝑂3 − 𝑁𝐸 + 𝑁𝑂3 − 𝑁𝑊𝐴𝑆 𝑁𝑂3 − 𝑁𝑥 + 𝑁𝑂3 − 𝑁𝑖𝑛 = 𝑁𝑂3 − 𝑁𝐸 + 𝑁𝑂3 − 𝑁𝑊𝐴𝑆 According to N.F.Gray (2005), Removal Efficiency=90% Since 𝑁𝑂3 − 𝑁𝑖𝑛 = 1200 Kg⁄day 𝑎𝑛𝑑 𝑎𝑠 𝑎𝑠𝑠𝑢𝑚𝑒𝑑 𝑁𝑂3 − 𝑁𝑥 = 5031.2 Kg⁄day 𝑇𝑜𝑡𝑎𝑙 𝑁𝑂3 − 𝑁𝑖𝑛 = 6231.2 Kg⁄day 𝑁𝑂3 − 𝑁 𝑟𝑒𝑚𝑜𝑣𝑒𝑑 𝑖𝑛 𝑎𝑒𝑟𝑎𝑡𝑒𝑑 𝑡𝑎𝑛𝑘 = 0.90 × 6231.2 Kg⁄day = 5608.08 Kg⁄day 𝑁𝑂3 − 𝑁𝐸 = 6231.2 Kg⁄day − 5608.08 Kg⁄day = 623.12 Kg⁄day 𝑁𝑂3 − 𝑁𝑊𝐴𝑆 = 623.12 Kg⁄day 𝑁𝑂3 − 𝑁𝑅 = 623.12 Kg⁄day
Page | 76
VIII.
Phosphorus Balance on the membrane skid
Overall Balance: [𝑇𝑜𝑡𝑎𝑙 𝑃ℎ𝑜𝑠𝑝ℎ𝑜𝑟𝑢𝑠 𝐸𝑛𝑡𝑒𝑟𝑖𝑛𝑔 𝑡ℎ𝑒 𝑠𝑦𝑠𝑡𝑒𝑚] = [𝑃ℎ𝑜𝑠𝑝ℎ𝑜𝑟𝑢𝑠 𝑙𝑒𝑎𝑣𝑖𝑛𝑔 𝑡ℎ𝑒 𝑠𝑦𝑠𝑡𝑒𝑚] + [𝑇𝑜𝑡𝑎𝑙 𝑃ℎ𝑜𝑠𝑝ℎ𝑜𝑟𝑢𝑠 𝑝𝑟𝑒𝑠𝑒𝑛𝑡 𝑖𝑛 𝑊𝐴𝑆] 𝑃𝑖𝑛 = 70 Kg⁄day = 1 g⁄m3 Assuming Efficiency of Phosphorus Removal is 65% 𝑃ℎ𝑜𝑠𝑝ℎ𝑜𝑟𝑢𝑠 𝑟𝑒𝑚𝑜𝑣𝑒𝑑 𝑖𝑛 𝑎𝑒𝑟𝑎𝑡𝑒𝑑 𝑡𝑎𝑛𝑘 = 65% × 70 Kg⁄day = 45.5 Kg⁄day = 0.65 g⁄m3 𝑃𝐸 = 70 Kg⁄day − 45.5 Kg⁄day = 24.5 Kg⁄day 𝑃𝑊𝐴𝑆 = 24.5 Kg⁄day 𝑃𝑅 = 24.5 Kg⁄day 3.2
Energy Balance
Heat transfer during cooling Biogas is a mixture of CO2, N2, O2, H2S and CH4, and with mole fraction of 0.258, 0.034, 0.005, 0.003 and 0.700 respectively. Assuming a steady flow process, the biogas is cooled from 308 to 293 K at a constant pressure of 0.102 MPa. Hence the heat transfer during the process will be evaluated as follows.
Page | 77
Additional assumptions This is steady-flow process since there is no change with time at any point and thus ∆mcv; change in mass of control volume and ∆Ecv; change in energy is equal to zero. The kinetic and potential energy changes are negligible. ∆mcv = ∆Ecv = 0 Analysis of system The cooler is considered as control volume since mass crosses the system boundary during the process. We will note that heat is transferred out of the system.
Furthermore while analyzing the critical properties of the various gases, we can notice that the O2, N2 and CH4 will remain above their critical temperature, but they are all below their critical pressures, and thus we can assume that the biogas behaves as an ideal gas and can be demonstrated using Kay’s rule (Boles et al., 2011) (refer to appendix Energy Balance to demonstrate that biogas can be considered as ideal gas via Kay’s rule).
36Table 3.1: Enthalpy of different gas components
The energy balance for this steady-flow system can be expressed on a unit mole basis as:
Page | 78
eout - eout = ∆esystem = 0 ein = eout → h1 = h2 + qout q”out = h1 – h2 (fore ideal gas) Where: ein= energy input, KJ eout = energy output, KJ ∆esystem = energy change of system, KJ h1 = enthalpy at initial temperature, KJ/Kmol h2 = enthalpy at final tempearature, KJ/Kmol q”out = heat transferred, KJ/Kmol q”out = h1 – h2 = yN2(h1 – h2) + yCO2 (h1 – h2) + yO2(h1 – h2) + yH2S(h1 – h2) + yCH4(h1 – h2) q”out = 0.034(8955.8-8520.88) + 0.258(9731.2-9175.88) + 0.005(8971-8532.63) + 0.003(8959.52-8468.63) + 0.7(6552.37-6363.84) Total mole of biagas = 307.517 kmol Total q”out = 91.7 GJ/day Chapter 4:
Mechanical sketches and schedules
Page | 79
3.33m
8m
A
A
3.38 m
2.25
University of Mauritius
Sketch of Top, Front & Side view of AIP oil-water separator
Beng(Hons) Chemical & Environmental Engineering(Level 3) Project Coordinator: Mr.A.K Ragen & Mr A.Mudhoo Project Supervisor: Mr A.Mudhoo
Design Project 2(CHE4101) Date: 01.04.15 Scale: Not to Scale
Size: A3
Drawn By:
SOOMAREE KESHAV
Group: 3A
ID:
1114132
Page | 80
88 m
42.5 m
Front View
Side view
University of Mauritius
The membrane bioreactor
Beng(Hons) Chemical & Environmental Engineering(Level 3) Project Coordinator: Mr.A.K Ragen & Mr A.Mudhoo
Project Supervisor: Mr A.Mudhoo
Design Project 2(CHE4101) Date: 01.04.15
Scale: Not to Scale
Size: A3
Drawn By:
SOOMAREE KESHAV
Group: 3A
ID:
1114132
Page | 81
University of Mauritius
Sketch of Top, Front & Side view of AIP oil-water separator
Beng(Hons) Chemical & Environmental Engineering(Level 3) Project Coordinator: Mr.A.K Ragen & Mr A.Mudhoo Project Supervisor: Mr A.Mudhoo
Design Project 2(CHE4101) Date: 29.03.15 Scale: Not to Scale
Size: A3
Drawn By:
SOOMAREE KESHAV
Group: 3A
ID:
1114132
Page | 82
University of Mauritius
Sketch of module membrane showing two distinct membranes
Beng(Hons) Chemical & Environmental Engineering(Level 3) Project Coordinator: Mr.A.K Ragen & Mr A.Mudhoo
Project Supervisor: Mr A.Mudhoo
Design Project 2(CHE4101) Date: 29.03.15
Scale: Not to Scale
Size: A3
Drawn By:
SOOMAREE KESHAV
Group: 3A
ID:
1114132
Page | 83
Chapter 5: 5.1
Material of Construction Material of construction for the membrane Bio-reactor Tank
The two possible construction materials for the MBR was be either steel or concrete. However the use of steel is deem to be more expensive and may require more frequent maintenance that a concrete basin. Furthermore while examining the volume of water to be handled by the tank and the subsequent pressure that will be exerted by the fluid which would be relative high; it is recommended to opt for a reinforced concrete structure. Reinforced concrete is ideal for the construction of the basin since the latter is a composite material of steel bars embedded in a hardened concrete matrix; concrete, assisted by steel carries the compressive forces while steel resist tensile forces. In addition concrete is a composite material. The dry mix consists of cement and coarse or fine aggregates. Water is added and this reacts with the cement which hardens and binds the aggregates into the concrete matrix; the concrete matrix sticks and binds on to the reinforcing bars (Choo et al., 1990). 5.2
Material of construction for the module membrane
The specific membrane area (membrane area per unit module volume) refers to the area based on the FS panel. The area per module (FS) or rack (HF) is given in parenthesis, where provided by the supplier. Abbreviations for membrane polymeric materials are: PAN:
polyacrylonitrile
PE:
polyethylene
PES:
polyethylsulphone
PS:
polysulphone
PVDF:
polyvinylidine difluoride
Page | 84
37Table 5.2.1: Membrane configuration definitions
HF or MT
Generic term
FS
Membrane Element
Single sheet, or part there Single filament/fibre or of Panel
tube Module
Multiple element
Module, cassette or stack
Cassette, stack or rack
Multiple multi-element
Train
Train
38Table 5.2.2: Membrane module details of FS
Supplier
Microdyne-Nadir
Membrane or module proprietary name (model) BioCel Membrane material
PES
Pore size (µm) or MWCO (kDa)
150 kDa
Panel dimensions, length x width x depth (mm)
1000 width x 5
Panel area (m2)
10
Membrane separation (mm)
8 (2 mm membrane thickness)
Module dimensions, length x width x depth 1200, 1340 x 650, 1140 x 1800, (mm)
2880
Number of panels per module
-
Total membrane area per module (m2/m3)
70 (90)
Clean water permeability (LMH/bar)
450–550
Supplier
Novasep Orelis
Membrane or module proprietary name (model)
Pleiade®
Membrane material
PAN
Pore size (µm) or MWCO (kDa)
40 kDa
Panel dimensions, length x width x depth (mm)
2610 x 438
Panel area (m2)
2
Page | 85
Membrane separation (mm)
3
Module dimensions, length x width x depth (mm) 2610 x 438 x 1710 Number of panels per module
-
Total membrane area per module (m2/m3)
(36)
Clean water permeability (LMH/bar)
1250 ± 500
Supplier
Toray Industries
Membrane or module proprietary name (model)
Toray (TRM140-100S )
Membrane material
PVDF
Pore size (µm) or MWCO (kDa)
0.08 µm
Panel dimensions, length x width x depth (mm)
1608 x 515 x 13.5 (inc. 6 mm separation)
Panel area (m2)
1.4
Membrane separation (mm)
6
Module dimensions, length x width x depth (mm) 2100 x 810 x 1620 Number of panels per module
50 , 100 or 200
Total membrane area per module (m2/m3)
135
Clean water permeability (LMH/bar)
-
39Table 5.2.3: Membrane module details of HF
Mitsubishi Rayon Engineering
Supplier Membrane
or
module
proprietary
name Sterapore SUR
(model) Membrane material
PE
Pore size (µm) or MWCO (kDa)
0.4 µm
Filament diameter
0.54 mm
Module dimensions, length x width x depth 1035 x 13 x 524 446 (mm) Module area (m2)
Up to 210
Page | 86
Number of filaments per element
-
Cassette dimensions, length x width x depth 1442 x 1538 x 725 (mm) Number of modules per cassette
70
Total membrane area per module (m2/m3)
485
Clean water permeability (LMH/bar)
-
Supplier
Polymem
Membrane or module proprietary name (model) Immem (WW120) Membrane material
PS
Pore size (µm) or MWCO (kDa)
300 kDa; 0.08 µm
Filament diameter
0.7 to 1.4mm
Module dimensions, length x width x depth 1000 to 1500 x 315 (mm) Module area (m2)
60–100m2
Number of filaments per element
a few tens of thousands
Number of modules per rack
Na
Total membrane area per module (m2/m3)
800
Clean water permeability (LMH/bar)
500
For this design the Microdyne-Nadir is chosen made up of polyethylsulphone with a total area of 10000 m2 and with 4 panels of area 10 m2 each having 40 panels per module as per calculation in chapter 2. 5.3
Material of construction for the oil-water separator
The oil-water separator is designed with coalescer plates which operates by method of physical alteration means. The material is of stainless steel. Most other designs utilize a shop-fabricated stainless steel frame or no frame system at all. The standard coalescer plates are typically polypropylene, pvc, or painted carbon steel. Plastic coalescer plates are heat sealed to form the pack and are set in the coalescer frame.
Page | 87
Carbon steel plate coalescer plates are typically stitch welded into the carbon steel coalescer frames and are not removable for cleaning. Coalescer materials that have been used include: polypropylene, pvc, cpvc, acrylic, aluminum, marine aluminum, 304 & 304L stainless steel, 316 and 316L stainless steel. Other materials such as phenolic epoxies composite materials show promise, as well. The coalescer designed in this project is to last the lifetime of the separator unit. The coalescer frame is built of sturdy structural stainless steel. The plate-holding strips are 304 stainless steel, as well. Marine aluminum and 316 stainless steel plate-holding strips are available for particular applications. The Multi-Pack can accommodate any flat plate material. 40Figure 5.3.1: Stainless steel oil-water separator
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CHAPTER 6: 6.1
Instrumentation and Control
Control Strategies for the Membrane Bio-reactor Process control and software 1. Feedback control and alarm triggering relies on monitoring of key parameters such as TMP (for indicating membrane fouling condition and triggering a cleaning cycle), DO (for biological process control) and turbidity (for membrane integrity). 2. Unless they are specifically designed to be free from clogging, it is essential that the maintenance schedule includes cleaning of the aerators. This can be achieved by flushing with a dilute hypochlorite solution. For some technologies the aerator flush is scheduled at the same time as the maintenance clean. 3. The principle impact of added process complexity is on the software and programmable logic controllers (PLCs), and on ancillary hardware such as pumps, valves and actuators. For example, intermittent aeration at 10 s means that each valve is actuated pneumatically over 3 million times per year. 4. Foaming control and abatement procedures are particularly important in an MBR since aeration is more intense than for an ASP. Designs should include surface wasting or spraying. 5. Sludge wasting for SRT control can be based on on-line MLSS measurement, although instruments have only recently developed for this. Pre-treatment and residuals management 1. The basic process can be modified in the same way as a conventional ASP to achieve denitrification, chemical phosphorous removal (CPR) and biological nutrient removal (BNR). Additional tanks (or tank volume) and sludge transfer pumps must then be sized accordingly, based on similar bio kinetic principles as those used for the design for the core aerobic process. 2. Pre-clarification can be used to reduce aeration demand (for agitation of
biomass) by reducing solids (“trash”) loading, but this significantly adds to footprint. Upgrading screens is essential, especially for HF iMBRs Grit removal is desirable for plants if no capacity is available to allow the grit to settle out before the membrane tank.
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3. MBR sludge is generally less settleable than ASP sludge, with floc sizes generally being smaller and sludge volume index (SVI) values higher. Conventional gravity thickening is therefore less effective for MBR sludge. Membrane thickening can and has been used for this duty, albeit operating at necessarily low fluxes. Tank sizing and redundancy 1. DO levels are _0.5 mg/L in the anoxic zone, typically 1.0–2.5 mg/L in the aerobic zone and relatively high in the membrane region (2–6 mg/L) where aeration is intensive. If recycling for denitrification takes place from the membrane aeration tank to the anoxic zone then the anoxic zone becomes slightly aerobic at the sludge inlets, reducing denitrification efficiency. To compensate for this the anoxic zone must be increased to extend the HRT in this region. Alternatively, sludge can be recycled from the aerobic tank. 2. Retrofitting places additional constraints on design of iMBRs, since the tank size determines the HRT and the shape and placement of immersed membrane modules. Retrofitting of side stream modules, on the other hand, is not constrained by the aeration tank dimensions. 3. Spare capacity is required for membrane cleaning, which either involves draining of the tank and cleaning in air or CIP. In the former case the biomass in the membrane train being cleaned has to be transferred either to a holding tank or to adjacent membrane tanks. In either case sufficient installed capacity is needed to contend with the total volume entering the works while the membrane train is being cleaned. For large plants with a large number of trains (membrane tanks) the cleaning can be sequenced to avoid large hydraulic shocks on the remaining in-service modules. For small plants a buffer tank may be required.
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V0
Pressure Sensor (0-4 bar absolute)
V4
F
Mass Flowmeter Permeate
V7
P
T
Feed
Suction Pump (0-4 L/hr)
Membrane Module
F
Massflowmeter
V5
V8
V9
P
V1
BackWash
Retenate
F
Feed/Backwash Pump V6
Pressure Sensor (0-4 bar absolute)
Flow Control
Mass Flowmeter
V2 Chemical Cleaning 1
V3
Chemical Cleaning 2
University of Mauritius
Sketch 1: Cleaning control of MBR
Beng(Hons) Chemical & Environmental Engineering(Level 3)
Project Coordinator: Mr.A.K Ragen & Mr A.Mudhoo Project Supervisor: Mr A.Mudhoo
Design Project 2(CHE4101)
Date: 3.06.15 Scale: Not to Scale
Size: A3
Drawn By:
SOOMAREE KESHAV
Group: 3A
ID:
1114132
Page | 91
4x0.405 l/d Excess Sludge
Concentrated Influent P1 = 0.075 l/min
Air V4
V2
V1
SV 4
V3 Overflow
PS 3
P
Over flow alarm
Tap Water
P2 =
P5 =
0.9 l/min
0.09 l/min (fil) – 0.3 l/min (BW)
PS 4
Degas vessel
P Emergency Overflow pH
Cooler
pH
DO
ORP
Cooler
Cooler
UF Membrane
V7
V6
Effluent grab sample
Over flow alarm
V8
Mixer SV 1
Aerobic/Anoxic zone Anaerobic zone
PS 2
Mixer
P SV 3
P
Permeate Over Flow
PS 1
P3 = 0.375 l/min
P4 = 7.651 l/min
V5 SV 2
University of Mauritius Beng(Hons) Chemical & Environmental Engineering(Level 3) Project Coordinator: Mr.A.K Ragen & Mr A.Mudhoo Project Supervisor: Mr A.Mudhoo
Backwashing Tank (7L)
Air 7.651 l/min
F2
Sketch 2: PID of MBR Date: 25.06.15 Scale: Not to Scale
Design Project 2(CHE4101) Size: A3 Drawn By: Group: 3A ID:
SOOMAREE KESHAV 1114132
Page | 92
Sewer
O2 P2
T
Ph
Computer
Sewer
P3 Peristaltic Pump Membrane
Demi water
Activated Sludge
NaOCl Permeate
Air
Mass Balance Peristaltic Pump Centrifugal Pump
Back Flush Pump
Damper
P1
F
University of Mauritius
Sketch 3: PID of Module membrane
Beng(Hons) Chemical & Environmental Engineering(Level 3) Project Coordinator: Mr.A.K Ragen & Mr A.Mudhoo Project Supervisor: Mr A.Mudhoo
Design Project 2(CHE4101) Date: 3.06.15 Scale: Not to Scale
Size: A3
Drawn By:
SOOMAREE KESHAV
Group: 3A
ID:
1114132
Page | 93
CHAPTER 7: 7.1
Safety Considerations
The oil-water separator
Personal Safety: 1. Toxic substances present in wastewater Deviation: High; Good State/ Bad state Possible causes: 1. Contact with the Wastewater 2. Needle stick injury when removing screenings from a bar screen
Consequences: 1. Chemicals absorbed through skin when in contact with wastewater. 2. Disease can also enter the body through cuts and abrasion Safeguard: Provide hand gloves and stay away from the wastewater Action: Assistance should be provided and immediate actions should be taken in case of Skin Contact 2. Cleaning and Maintenance Deviation: Clean/ Unclean; Good State/ Bad state Possible causes: Screen blockage or clogging Consequences: 1. Efficiency of screens decreases 2. Wastewater unable to pass through causing overflow Safeguard: 1. Two- stage screen in order to facilitate safe cleaning; to reduce the possibility of blockage 2. To allow proper maintenance
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Action: 1. Provide a sensor and an alarm to monitor the risks of blockage 2. Regular checkup and maintenance should be done 7.2
The Membrane Bioreactor
Safety Parameters: Construction and maintenance Deviation: High Possible causes: Safety rules and regulations not properly abided Consequences: 1. Falling into the ponds causing injuries 2. Disease caused by infectious agents like protozoa, virus upon skin contact 3. Chronic poisoning by inhalation Safeguard: 1. Hand railing provided at all places where there is potential of falling around all tanks and other places where falling height is greater than 1.5m 2. Use of life buoys and Safety jackets to get the person out of water Action: Emergency measures should be provided; provide with protective clothing and other personal protective equipment and chemical resistant clothing to avoid exposure of skin
CHAPTER 8: 8.1
Review of the final design
Summary of key Deviations
One of the key deviations for detailed design is that there is a change the initial wastewater flow-rate from 200000 m3/day to 75000 m3/day. The additional deviations and amendments can be noted for the equalization tank design and biogas upgrading system. Furthermore errors were noted in the mass balance of the preliminary design for the biogas upgrading system, the oil and grease separator and coarse screen which lead to several
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key mistakes in the preliminary design and had a domino effect in the subsequent calculations, thus it is obvious that while the comparing the mass balance of the preliminary and detailed these variation can be easily noted. Hence to avoid repetitions we shall review mostly the sizing of various equipment. 8.2
Review of API Separator
Preliminary Design
Detailed Design
Cross-sectional area = 54m2
Minimum
Reason/Comments
vertical
cross
sectional area = 60 m²
The key variation is lies in
Depth of channel = 3.38 m
Depth of channel = 3.6 m
these
Length of separator = 3.33 m
Length of separator = 3.33 m
parameters
Width of channel = 8 m
Width of channel = 8 m
Number of channels = 4
Number of channels = 4
Retention time = 30 min
Retention time = 30 min
Construction Material : Steel
Construction material: Stainless steel
Not considered
Rise rate of oil globules 0.263
Not considered
Velocity = 3 ft/min
Not considered
Area of single channel = 14.9 m²
Not considered
8.3
Length of forebay= 14.2 m
Review of the membrane bioreactor
The Reactor Number of tanks
1
Depth (m)
4.4
Length (m)
42.5
Width(m)
88 Fine bubble ceramic diffuser
Aeration system
Oxygen
demand
=
1565.40 𝑚3 𝑜𝑓 𝑂2⁄𝑑𝑎𝑦
Page | 96
Air pipe diameter (m)
0.32
Length of air pipe(m)
30
Power required (KPa)
2.28
Number of centrifugal blowers
1 (+1 as back up)
Inlet pipe
0.164
Effluent pipe Effluent box(m)
0.438 4x3
Aeration period
5.12 Hr
Diffuser submergence(m)
7
Oxygen transfer efficiency (OTE)
35%
Aeration configuration
Covering the floor completely
Air supply SRT
Using a centrifugal blower feeding 7454.24 𝑚3 𝑜𝑓 𝑎𝑖𝑟⁄𝑑𝑎𝑦 10 days
BOD vol. loading F/M
0.938
𝐾𝑔 𝑚3 . 𝑑𝑎𝑦
0.3
The membrane Module Am
9887 m2
Area per element
250 m2
Actual membrane area
10000 m2
Number of elements
40
K’
120 N LMH/bar
Jnet
21 LMH
Jnet,actual
20 LMH
J’net,actual
25 N LMH
J’b
42 N LMH
J’actual
30 N LMH
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CHAPTER 9: 9.1
ECONOMICS OF THE PROJECT, AS DESIGNED
Total purchase equipment cost
This represents the basis for estimating the capital investment for a chemical plant. The cost of all the main equipments in the treatment plant, namely, the UV reactors ,the biogas upgrading system, API Separator, and among other ; likewise some equipment cost were estimated by scaling. The Marshall and Swift equipment cost index was used to obtain the present time costs of the equipment. Total purchase equipment cost = Rs. 159,268,246 9.2
Total capital investment (TCI)
This is a very large amount of money that is initially invested before the start of operation of a plant and this is normally used to purchase land and purchase installation of machinery and equipment. As soon as land has been purchased and made available and services must be obtained, the plant is set-up with all the necessary that pilings, controls and services. It should be noted that money will also be needed to pay for expenses incurred for the operation of the plant. The money needed for setting up the plant is known as the Capital Investment. Capital Investment is the total amount of money needed to supply the necessary plant and manufacturing facilities plus the amount of money required as working as working capital and operation of the facilities. Total Capital investment is calculated as: TCI = FCI + WC Where: TCI - Total Capital Investment FCI - Fixed Capital Investment WC - Working Capital This represents the sum of the fixed capital investment and the working capital. Working capital = Rs. 19,582,968 Fixed capital investment is the sum of the direct and indirect costs. The direct cost consists of expenses on the land, the purchased equipment, the instrumentation and controls, the piping and electrical systems, among others while the indirect costs are
Page | 98
expenses which are not directly involved with material and labor of the installation of the plant. 9.3
Total product cost
It represents the sum of the manufacturing cost and the total general expenses. The manufacturing cost is given by the sum of the direct production costs, the fixed charges and the plant overheads. The direct production costs include the costs of raw materials; however for our treatment plant no raw material will be needed, operating labor, laboratory charges and maintenance. Total product cost = Rs. 160, 596,085 The fixed charges are expenses pertaining to depreciation, taxes and insurance. Fixed charges = Rs. 34,812,057 Plant overheads = Rs. 16,059,608 Manufacturing cost = Rs. 138,112,633 The administrative costs, the distribution and selling costs, the research and development costs and interests constitute the general expenses. General expenses = Rs. 22,483,452 Total product cost = Rs. 160,596,085 9.4
Total revenue
For income for the treatment plant will shall consider the sales of treated water for irrigation and the sludge cake for composing. Likewise the treated water and sludge cake will be sold at Rs 0.5/m3 and Rs 25/kg respectively. On a yearly basis, the plant produces 26.65×106 m3of water and 26.44×106 kg of sludge. Thus, Total revenue = Rs. 277, 788,095 9.5
Gross earning cost
This represents the gross profit made by the power plant. It is calculated by the difference of the total income and the total product cost. Gross earning = Rs. 99,613,209
Page | 99
9.6
Pay-back period
Payback can be described as the period of time required for the return on an investment, that is, the time required to recover the initial investment. The simple payback period method is when time value of money is not considered while for the discounted payback method, the time value of money is considered. The payback period indicates whether to go for a specific project or not (Sinnott et al., 2003).
Pay-back period = 7.427 years
9.7
The rate of return
In the case of bank loan, the future return takes the form of interest plus repayment of the principal. This is known as the loan cash flow. While in the case of the fixed asset, the future return takes the form of profits generated by productive use of the asset. This is called project cash flow. Rate of return is also known as Internal Rate of Return, IRR and is the rate at which one is recovering his investment.
This is the rate at which profit is made with respect to the initial investment. The latter would include charges on labour resource. The power plant constitute of 32 personnel. Taking into account all charges and the profit made, Rate of return = 11.4%.
9.8
The Net Present Value (NPV) and Initial Rate of Return (IRR)
The net present value is the harmonization of net cash flows of different period of time at a common time period. The common time period is usually the time the project starts, that is the present time. It is the conversion of future cash flows into present time at a given rate of return. Normally, the net present value of the project is then the difference between the present value of the annual cash flows and the initial required investment.
Page | 100
Present value of the expected cash flows is computed by discounting them at the required rate of return. Net present value is a calculation that compares the amount invested today to the present value of the future cash receipt from the investment. The following parameters are important while calculating NPV: - Rate of return (IRR) - Service life of project or equipment - Annual cash inflow over service life. - Annual cash outflow over service life. - Net cash flows (profits/savings) over service life NPV is the present value of the future cash inflows. NPV= Rs. 1,293,424,747 IRR represents the true interest rate on an investment over the course of its economic life. IRR = 30.45 % 41Table 9.0: Summary of the economics of the treatment power plant
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CHAPTER 10:
Environmental Concerns
Even wastewater treatment ensures that not much great demands are been made on the environment and is a step forward towards safeguarding the ecological and marine resources, in particular surf water and ground water and as well as improve sanitation and protect public health. And similarly, the option for wastewater treatment and reuse makes provision for long term water reliability within the community by providing substitute for fresh water and also is a plus-point for water demand and drought management in overall water resources planning; it is be noted that a during the treatment there is a significant amount of waste which is cause for concerns. The table below summaries the various type of waste generated and their related mitigation measure for their resulting nuisance. Waste generated
Source
Treatment of waste/ emissions
Screenings (consisting of Coarse screen
Screenings will be disposed to
large
the landfill without grinding or
debris,
leaves,
plastics,
washing
floatable
Since washing will generate more
materials amongst others)
wastewater thus is not advisable.
Page | 102
Other
alternatives
such
as
incineration may be considered if not too costly. Scum
Activated sludge Scum from the final clarifier are system
scrapped by means of scrappers
Secondary
before
settling tank
discharged to the landfill which
they
are
collected
and
represents a safe, easy and cost effective method of disposal. Sludge in terms of Oil & API grease,
Oil/Water Since oil and grease from API
Separator
COD
cannot sent to land field due to high risk of soil contamination it would trucked to a solid treatment processing plant or send to a processing factor for oil recovery
Sludge
Dry sludge
Primary clarifier
Since the sludge produced have
MBR
considerable amount of BOD.
Secondary
COD and TSS, they will be sent
clarifier
to a digester for stabilization
Drying Bed
Compost plant is the best and most viable mean of disposal
Biogas
Sludge Digester
The biogas is the most valuable waste
Bioreactor
generated, since it has a huge energy potential it will be upgraded and use as fuel of plant’s boilers.
CHAPTER 11:
Conclusion
The aim of this project was to produce a detailed chemical engineering design of a wastewater treatment plant. I was assigned to design the membrane biological reactor
Page | 103
and the Oil-Water separator which required an extensive knowledge of heat & Mass transfer, thermodynamics, Unit operations, wastewater management, chemical process design Chemical economics, Chemical process safety and fluid mechanics. Most of these topics had already been covered during previous years of the undergraduate course and the rest are still ongoing. Indeed, the design also required important decisions to be taken in areas of uncertainty. All the reasoning behind any assumption and decision taken were explained explicitly. To conclude, we can eventually say that there are significant difference in between the primary design and that of the detailed one, especially in terms of sizing and costing. This design project has brought in me many practical skills and knowledge, giving a wider view on the job functions of chemical and environmental engineers.
References 1. Adham, S., DeCarolis, J.F. and Pearce, W. (2004) Optimisation of various MBR systems for water reclamation – phase III, Desalination and Water Purification Research and Development Program Final Report, No. 103. 2. Babcock,
R.
(2005)
www.wrrc.hawaii.edu/research/project_babcock/Babcockmembrane.
htm
(Accessed March 2015). 3. Benham, B.L., Brannan, K.M., Yagow, G., Zeckoski, R.W., Dillana, T.A., Mostaghimi, S. and Wynn, J.W. (2005) Development of bacteria and benthic total maximum daily loads: a case study, Linville Creek, Virginia. J. Environ. Qual., 34, 1860–1872. 4. Blatchley III, Ernest R., Bastian, K. Chad, Duggirala, Ravi K., Alleman, James E., Moore, Mark, Schuerch, Peter.,1996. “Ultraviolet irradiation and chlorination/dechlorination
for
municipal
wastewater
disinfection:
Assessment of performance limitations.” Water Environment Research, 68, 194204.
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5. Botha, G.R., Sanderson, R.D. and Buckley, C.A. (1992) Brief historical review of membrane development and membrane applications in wastewater treatment in Southern Africa. Wat. Sci. Technol., 25(10), 1–4. 6. C.J. Geankoplis, 1993, Transport Processes and Unit operations, 3rd Edition, India, Prentice Hall Inc 7. Cengel.Y.A , Boles.M.A, 2010, Thermodynamics An Engineering Approach, 7th Edition, New York, Mc Graw Hill. 8. DAR LIN, S.D.L., 2007. Water and Wastewater Calculations Manual. 2nd. New York: McGraw- Hill Companies, Inc. 9. Dieter Deublein and Angelika Steinhauser, 2008, Biogas from Waste and Renewable Resources An introduction 1st edition WILEY-VCH Verlag GmbH & Co. KGaA 10. Digest
of
energy
and
water
statistics
2011
available
at:
http://www.gov.mu/portal/goc/cso/report/natacc/DigestEnergy.pdf
,
accessed on 3 Jan 2013 11. DiGiano, F.A., Andreottola, G., Adham, S., Buckley, C., Cornel, P., Daigger, G.T., Fane, A.G., Galil, N., Jacangelo, J., Alfieri, P., Rittmann, B.E., Rozzi, A., Stephenson, T. and Ujang, Z. (2004) Safe water for everyone: membrane bioreactor technology. www.scienceinafrica.co.za/2004/june/membrane.htm 12. Frost and Sullivan (2003) MBR: A buoyant reaction in Europe, Report, June 2003, Frost and Sullivan. 13. Frost and Sullivan (2005) European report: introduction and executive summary, Report, August 2005, Frost and Sullivan. 14. G.Tchobanoglous,F.L.Burton, H.David Stensel, 2004, Metcalf and Eddy Wastewater Engineering Treatment and Reuse, 4th Edition, New York, McGraw Hill. 15. Göbel, A., Thomsen, A., McArdell, C.S., Joss, A. and Giger, W. (2005) Occurrence and sorption behavior of sulfonamides, macrolides and trimethoprim in conventional activated sludge treatment including sorption to sewage sludge. Environ. Sci. Technol., 39, 3981–3989.
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16. Hanzon, B.D and Vigilia, R. “Two Experts Offer Practical Guidance in Designing
and
Operating
Ultraviolet
Disinfection
Systems,”
Water
Environment and Technology, November 1999, pp. 35- 42. 17. Ho, Chu-Fei H., Pitt, Paul, Mamais, Daniel, Chiu, Carolyn, and Jolisw, Domenéc.,1998. “Evaluation of UV disinfection systems for large-scale secondary effluent.” Water Environment Research, 70 (6), 11421150. 18. Huber, M.M., Goebel, A., Joss A., Hermann N., Kampmann M., Löffler D., McArdell, C.S., Ried A., Ternes, T.A. and von Gunten, U. (2005) Oxidation of pharmaceuticals during ozonation of municipal wastewater effluents: a pilot study. Environ. Sci. Technol., 39, 4290–4299. 19. J. F. Richardson, J. H. Harker, J. M. Coulson, 1977, “Coulson and Richardson’s CHEMICAL ENGINEERING Fluid flow, Heat transfer and Mass transfer”, Volume 1, 3rd Edition. UK, Pergamon Press 20. J. F. Richardson, J. H. Harker, J. R. Backhurst, 2002, “Coulson and Richardson’s CHEMICAL ENGINEERING Particle, Technology and Separation Processes”, Volume 2, 5th Edition. UK, Elsevier Jaime Benítez, 2009, Principle and Modern Applications of Mass Transfer Operations, 2nd Edition, New Jersey, John Wiley and Sons 21. Joss, A., Andersen, H., Ternes, T., Richle, P.R. and Siegrist, H. (2004) Removal of estrogens in municipal wastewater treatment under aerobic and anaerobic conditions: consequences for plant optimisation. Environ. Sci. Technol., 38(11), 3047–3055. 22. Joss, A., Keller, E., Alder, A., Göbel, A., McArdell, C.S., Ternes, T. and Siegrist, H. (2005) Removal of pharmaceuticals and fragrances in biological wastewater treatment. Water Res., 39(14), 3139–3152. 23. Joss, A., Zabczynski, S., Göbel, A., Hoffmann, B., Löffler, D., McArdell, C.S., Ternes, T.A., Thomsen, A. and Siegrist, H. (2006) Biological degradation of pharmaceuticals in municipal wastewater treatment: proposing a classification scheme. Water Res., 40(8), 1686–1696.
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24. Kennedy, S. and Churchouse, S.J. (2005) Progress in membrane bioreactors: new advances, Proceedings of Water and Wastewater Europe Conference, Milan, June2005. 25. Lawrence, D., Ruiken, C., Piron, D., Kiestra, F. and Schemen, R. (2005) Dutch MBR Development: Reminiscing the Past Five Years, H2O, 36–29. Metcalf, Eddy. (2003) Wastewater Engineering – Treatment and Reuse (3rd edn). McGraw-Hill, New York. 26. Maxwell, S. (2005) the state of the water industry 2005, a concise overview of trends and opportunities in the water business, The Environmental Benchmarker and Strategist Annual Water Issue. 27. Qin, J.-J., Kekre, K.A., Guihe, T., Ooa, M.-H., Wai, M.-N., Lee, T.C., Viswanath, B. and Seah, H. (2005) New option of MBR-RO process for production of NEWater from domestic sewage. J. Membrane Sci. 28. Schyns, P., Petri, C., van Bentem, A. and Kox, L. (2003) MBR Varsseveld, a Demonstration of Progression, H2O, 10–12. 29. Tao, G., Kekre, K., Wei, Z., Lee, T.C., Viswanath, B. and Seah, H. (2005) Membrane bioreactors for water reclamation. Water Sci. Technol., 51(6–7), 431– 440. 30. Ternes, T.A., Joss, A. and Siegrist, H. (2004) Scrutinizing pharmaceuticals and personal care products in wastewater treatment. Environ. Sci. Technol., 38(20), 393A–399A. 31. Van der Roest, H.F., Lawrence, D.P. and van Bentem, A.G.N. (2002) Membrane Bioreactors for Municipal Wastewater Treatment. IWA Publishing. 32. Voet Donald and Voet Judith G., 1995. Biochemistry. 2 Nd ed. New York:John Wiley & Sons, Inc., New York. 33. WEF (2006) Membrane systems for wastewater treatment. Water Environment Foundation, WEFPress/McGraw-Hill, New York. 34. Yang, W., Cicek, N. and Ilg, J. (2006) State-of-the-art of membrane bioreactors: worldwide research and commercial applications in North America. J. Membrane Sci., 270, 201–211.
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Appendices Appendices A: Mass Balance Mass Balance for the MBR
Overall Balance around the MBR Influent = Waste Sludge + Effluent
Q = Influent Flowrate
SE = BOD in Effluent, 𝑚𝑔⁄𝐿
S0 = BOD in influent, 𝑚𝑔⁄𝐿
Hence BOD efficiency can be calculated as follows: Given: BOD in domestic wastewater entering Primary Settling Tank = 307 𝑚𝑔⁄𝐿 Assuming BOD removal efficiency in primary clarifier = 40 % Primary effluent BOD = 307 𝑚𝑔⁄𝐿 × (1 − 0.40) = 184 𝑚𝑔⁄𝐿 Therefore; As assumed permissible limits, that is 40 mg/L = 2800 kg/day is in the effluent
Page | 108
BOD Removal Efficiency in MBR =
184 𝑚𝑔⁄𝐿 −40𝑚𝑔⁄𝐿 184𝑚𝑔⁄𝐿
× 100 = 78%
Hence; 307 𝑚𝑔⁄𝐿 − 40 𝑚𝑔⁄𝐿 𝑂𝑣𝑒𝑟𝑎𝑙𝑙 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑟𝑦 = ( ) × 100 = 87% 307 𝑚𝑔⁄𝐿 The recycle ratio can be expressed as follows: 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝑅𝑎𝑡𝑖𝑜 =
𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝐹𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑚3 ⁄𝑑𝑎𝑦 𝐼𝑛𝑓𝑙𝑢𝑒𝑛𝑡 𝐹𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑚3 ⁄𝑑𝑎𝑦
Typical recycle ratio for conventional activated sludge process = 0.25 – 0.50 Average Recycle Ratio = 0.375 Therefore; 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝐹𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑄𝑅 = 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝑟𝑎𝑡𝑖𝑜 × 𝐼𝑛𝑓𝑙𝑢𝑒𝑛𝑡 𝑓𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑄0 = 0.375 × 70000 𝑚3 ⁄𝑑𝑎𝑦 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝐹𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑄𝑅 = 26250 𝑚3 ⁄𝑑𝑎𝑦 Also by the methodology of Shu Dar lin (2005), 𝑄𝑅 can be expresses as follows: 𝑄𝑅 =
𝑄0 (𝑥 − 𝑥0 ) 𝑥𝑤 − 𝑥
Whereby: X = MLSS concentration, 2500 𝑚𝑔⁄𝐿 X0 = Primary Effluent TSS, 102.6 𝑚𝑔⁄𝐿 𝑄𝑟 = 𝑟𝑒𝑐𝑦𝑐𝑙𝑒 𝑓𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 26250 𝑚3 ⁄𝑑𝑎𝑦 26250 𝑚3 ⁄𝑑𝑎𝑦 =
70000 𝑚3 ⁄𝑑𝑎𝑦 (2500 𝑔⁄𝑚3 − 102.6 𝑔⁄𝑚3 ) 𝑥𝑤 − 2500 𝑔⁄𝑚3
𝑥𝑤 = 3893.07 𝑔⁄𝑚3 Also; 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝑅𝑎𝑡𝑖𝑜 =
𝑄𝑅 𝑋 = 𝑄0 𝑋𝑅 − 𝑋
Page | 109
Whereby: 𝑋𝑅 is the concentration in recycle sludge and as assumed R is 0.375. 2500 𝑔⁄𝑚3 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝑅𝑎𝑡𝑖𝑜 = 𝑋𝑅 − 2500 𝑔⁄𝑚3
Inlet Flowrate:XO = Concentration of TSS in influent Primary Settling Tank Outlet Flowrate:Xe = Concentration of Biomass in effluent Return Sludge: QR = return flow pumping rate, 𝑚3 ⁄𝑑𝑎𝑦 Xu = return microorganism concentration Waste Activated Sludge: QW = Waste flow from recycle waste line, 𝑚3 ⁄𝑑𝑎𝑦 And µ = growth of solids (𝑑𝑎𝑦 −1 ) BOD Balance around MBR 𝐼𝑛𝑝𝑢𝑡 − 𝑜𝑢𝑡𝑝𝑢𝑡 + 𝑔𝑒𝑛𝑒𝑟𝑎𝑡𝑖𝑜𝑛 = 𝑎𝑐𝑐𝑢𝑚𝑢𝑙𝑎𝑡𝑖𝑜𝑛 (𝑄0 𝑆0 + 𝑄𝑅 𝑆𝐸 ) − (𝑄0 + 𝑄𝑅 )𝑆𝐸 −
𝜇𝑋𝑉 𝑑𝑆 = 𝑉 𝑌 𝑑𝑡
𝑑𝑆 𝑉=0 𝑑𝑡 Y = cell yield in kg MLSS/ kg BOD removed At steady state 𝜇𝑋𝑉 = 𝑄0 𝑆0 − 𝑄0 𝑆𝐸 𝑌 𝜇 𝑄0 (𝑆0 − 𝑆𝐸 ) = 𝑓⁄𝑚 𝑟𝑎𝑡𝑖𝑜 = 𝑌 𝑉𝑥 𝑆0 = 184 𝑚𝑔⁄𝐿 Assuming no chemical changes occur: 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝐵𝑂𝐷𝐸 = 40 𝑚𝑔⁄𝐿
Page | 110
Therefore: 𝐵𝑂𝐷𝑅 = 𝐵𝑂𝐷𝑊𝐴𝑆 = 40 𝑚𝑔⁄𝐿 Flow Balance Influent Flow Q0 = 70,000 m3/day Initial BOD = BOD0 = 184 g/m3 As calculated: BOD Efficiency = 78 % BOD in Effluent = 40 g/m3 Solid Balance on membrane 𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑇𝑆𝑆 𝑖𝑛 𝑅𝐴𝑆 = 𝑇𝑆𝑆𝑅 = 𝑋𝑈 𝑔⁄𝑚3 × 𝑄𝑅 𝑚3 ⁄𝑑𝑎𝑦 𝑇𝑆𝑆𝑅 = 10.65 𝑘𝑔⁄𝑚3 × 26250 𝑚3 ⁄𝑑𝑎𝑦 = 279,562.5 𝐾𝑔⁄𝑑𝑎𝑦 𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑇𝑆𝑆 𝑖𝑛 𝑊𝐴𝑆 = 𝑋𝑢 𝑘𝑔⁄𝑚3 × 𝑄𝑊 𝑚3 ⁄𝑑𝑎𝑦 = 2367.07 𝐾𝑔⁄𝑑𝑎𝑦 Assume TSS Removal Efficiency = 81% Therefore: 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑂𝑓 𝑇𝑆𝑆 𝑖𝑛 𝐸𝑓𝑓𝑙𝑢𝑒𝑛𝑡 = 0.19 × 102.6 𝑚𝑔⁄𝐿 = 19.494 𝑚𝑔⁄𝐿 = 1364.6 𝐾𝑔⁄𝑑𝑎𝑦 Balance on VSS on membrane The removal efficiency of VSS in an MBR system is 90%, therefore; 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑉𝑆𝑆 𝑖𝑛 𝐸𝑓𝑓𝑙𝑢𝑒𝑛𝑡 = 10% × 82.08 𝑔⁄𝑚3 = 8.208 𝑔⁄𝑚3= 574.6𝐾𝑔⁄𝑑𝑎𝑦 Whereby VSS = 80% TSS = 82.08𝑔⁄𝑚3 =5745.6𝐾𝑔⁄𝑑𝑎𝑦 Assuming: 𝑉𝑆𝑆𝑊𝐴𝑆 = 𝑉𝑆𝑆𝑅 = 5745.6 𝐾𝑔⁄𝑑𝑎𝑦 − 574.6 𝐾𝑔⁄𝑑𝑎𝑦 = 5171.04 𝐾𝑔⁄𝑑𝑎𝑦 NH3-N Balance on the membrane skid Overall Balance: 𝑁𝐻3 − 𝑁𝑖𝑛 = 𝑁𝐻3 − 𝑁𝑜𝑢𝑡
Page | 111
𝑁𝐻3 − 𝑁𝑂𝑈𝑇 = 𝑁𝐻3 − 𝑁𝐸 + 𝑁𝐻3 − 𝑁𝑊𝐴𝑆 By the methodology of N.F.Gray, 2005, the removal efficiency of 𝑁𝐻3 − 𝑁 in an ASP system is 90% 𝑁𝐻3 − 𝑁𝑖𝑛 = 1400 𝐾𝑔⁄𝑑𝑎𝑦 𝑁𝐻3 − 𝑁 𝑟𝑒𝑚𝑜𝑣𝑒𝑑 𝑖𝑛 𝑎𝑒𝑟𝑎𝑡𝑒𝑑 𝑡𝑎𝑛𝑘 = 90% × 1400 𝐾𝑔⁄𝑑𝑎𝑦 = 1260 𝐾𝑔⁄𝑑𝑎𝑦 𝑁𝐻3 − 𝑁𝐸 = 𝑁𝐻3 − 𝑁𝑊𝐴𝑆 = 𝑁𝐻3 − 𝑁𝑅 = 1400 𝐾𝑔⁄𝑑𝑎𝑦 − 1260 𝐾𝑔⁄𝑑𝑎𝑦 = 140 𝐾𝑔⁄𝑑𝑎𝑦 NO3-N Balance on membrane skid Overall Balance: 𝑁𝑂3 − 𝑁𝑖𝑛 = 𝑁𝑂3 − 𝑁𝑜𝑢𝑡 Since nitrification occurs, let 𝑁𝑂3 − 𝑁𝑥 be the amount of nitrates obtained by the nitrification of ammonia. Therefore: 𝑁𝑂3 − 𝑁𝑖𝑛 = 𝑁𝑂3 − 𝑁1 + 𝑁𝑂3 − 𝑁𝑥 Assuming 𝑁𝑂3 − 𝑁𝑥 = 5031.2 Kg⁄day 𝑁𝑂3 − 𝑁𝑜𝑢𝑡 = 𝑁𝑂3 − 𝑁𝐸 + 𝑁𝑂3 − 𝑁𝑊𝐴𝑆 𝑁𝑂3 − 𝑁𝑥 + 𝑁𝑂3 − 𝑁𝑖𝑛 = 𝑁𝑂3 − 𝑁𝐸 + 𝑁𝑂3 − 𝑁𝑊𝐴𝑆 According to N.F.Gray (2005), Removal Efficiency=90% Since 𝑁𝑂3 − 𝑁𝑖𝑛 = 1200 Kg⁄day 𝑎𝑛𝑑 𝑎𝑠 𝑎𝑠𝑠𝑢𝑚𝑒𝑑 𝑁𝑂3 − 𝑁𝑥 = 5031.2 Kg⁄day 𝑇𝑜𝑡𝑎𝑙 𝑁𝑂3 − 𝑁𝑖𝑛 = 6231.2 Kg⁄day 𝑁𝑂3 − 𝑁 𝑟𝑒𝑚𝑜𝑣𝑒𝑑 𝑖𝑛 𝑎𝑒𝑟𝑎𝑡𝑒𝑑 𝑡𝑎𝑛𝑘 = 0.90 × 6231.2 Kg⁄day = 5608.08 Kg⁄day 𝑁𝑂3 − 𝑁𝐸 = 6231.2 Kg⁄day − 5608.08 Kg⁄day = 623.12 Kg⁄day 𝑁𝑂3 − 𝑁𝑊𝐴𝑆 = 623.12 Kg⁄day 𝑁𝑂3 − 𝑁𝑅 = 623.12 Kg⁄day
Page | 112
Phosphorus Balance on the membrane skid Overall Balance: [𝑇𝑜𝑡𝑎𝑙 𝑃ℎ𝑜𝑠𝑝ℎ𝑜𝑟𝑢𝑠 𝐸𝑛𝑡𝑒𝑟𝑖𝑛𝑔 𝑡ℎ𝑒 𝑠𝑦𝑠𝑡𝑒𝑚] = [𝑃ℎ𝑜𝑠𝑝ℎ𝑜𝑟𝑢𝑠 𝑙𝑒𝑎𝑣𝑖𝑛𝑔 𝑡ℎ𝑒 𝑠𝑦𝑠𝑡𝑒𝑚] + [𝑇𝑜𝑡𝑎𝑙 𝑃ℎ𝑜𝑠𝑝ℎ𝑜𝑟𝑢𝑠 𝑝𝑟𝑒𝑠𝑒𝑛𝑡 𝑖𝑛 𝑊𝐴𝑆] 𝑃𝑖𝑛 = 70 Kg⁄day = 1 g⁄m3 Assuming Efficiency of Phosphorus Removal is 65% 𝑃ℎ𝑜𝑠𝑝ℎ𝑜𝑟𝑢𝑠 𝑟𝑒𝑚𝑜𝑣𝑒𝑑 𝑖𝑛 𝑎𝑒𝑟𝑎𝑡𝑒𝑑 𝑡𝑎𝑛𝑘 = 65% × 70 Kg⁄day = 45.5 Kg⁄day = 0.65 g⁄m3 𝑃𝐸 = 70 Kg⁄day − 45.5 Kg⁄day = 24.5 Kg⁄day 𝑃𝑊𝐴𝑆 = 24.5 Kg⁄day 𝑃𝑅 = 24.5 Kg⁄day
Appendix B: Energy Balances Power requirement for the Membrane Bioreactor In order to meet the oxygen demand in the aeration tanks, diffusers are placed and these diffusers require energy. Energy Balance on Aeration Tank Normally the newer technology include centrifugal blowers or positive displacement blowers, since positive displacement blowers is limited to only 425 m3/min volumetric flow rate and centrifugal blowers can be used for volumetric flow rate beyond 80 m3/min, a centrifugal pump is preferred in this case. By the methodology of Frank R. Spellman (2013), the power requirement for aeration is calculated as follows: Average power required for aeration = Pav =
QxRxT x [(Pdis /P) 0.283– 1] 3600 x 29.7 x 0.283 x η
Whereby:
Page | 113
P is the atmospheric pressure Q is the air flow rate T is the inlet temperature in Kelvin (280C = 301.15 K) η is the efficiency of the blower which is normally within the range 70%-80% R is the gas constant, 8.314kJmol-1K-1 Pdis = discharge pressure of blower which varies between 1.7 and 2.4 bar for fine bubble diffusers. Therefore: 1,447.22 𝑚3 ⁄𝑚𝑖𝑛 x 8.314 x 301.15 K 2.05 𝑏𝑎𝑟 0.283 Pav = x [( ) – 1] 3600 x 29.7 x 0.283 x0.75 1.01325 𝑏𝑎𝑟 Pav = 35.24 x 24 = 845.76 kWh/d Energy Balance on membrane bio filter Using the equation:𝑇 = 𝑤𝑅 2 Whereby: T is the torque in Kg.m W is the work kg/m R is the radius of the clarifier, m Assuming W = 20 lb/ft, W = 20 x 1.49 = 29.8 kg/m Since Diameter of clarifier = 26m Radius of clarifier, R = 13 m Hence; kg
𝑇 = 29.8 m × 13.02 𝑚2 = 5036.2 𝐾𝑔. 𝑚 = 49,405.12 𝑁𝑚 𝑃𝑜𝑤𝑒𝑟 = 𝑇𝑜𝑟𝑞𝑢𝑒 × 𝐴𝑛𝑔𝑢𝑙𝑎𝑟𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 = 𝑇 ×
𝐿𝑖𝑛𝑒𝑎𝑟𝑆𝑝𝑒𝑒𝑑 𝑟𝑎𝑑𝑖𝑢𝑠
From N.F Gray (2005), the speed of rakes varies between 3-6m/min and taking an average speed; Speed of rake = 4.5m/min = 0.075m/s
Page | 114
𝐴𝑛𝑔𝑢𝑙𝑎𝑟𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 =
Speed of rake 0.075 𝑚⁄𝑠 = = 0.00577 𝑟𝑎𝑑⁄𝑠 𝑟𝑎𝑑𝑖𝑢𝑠 13.0𝑚
Hence: 𝑃𝑜𝑤𝑒𝑟 = 49,405.12 𝑁𝑚 × 0.00577 𝑟𝑎𝑑⁄𝑠 = 285.07 𝑥 24 = 6841.68 𝑊ℎ/𝑑 Since 6 clarifiers are used, overall power requirements= 6841.68 x 6 = 41.05 kWh/d Energy balance on the amount of pumps As illustrated in the process flow diagram, 13 pumps are being used, therefore, the energy required by the pumps are calculated as follows: Number of pumps= 12 centrifugal pumps which operate 24 hours + 1 centrifugal blower which operate only 5.12 hours /day The wattage of the centrifugal pump = 25.1 kW Energy required = (12 × 25.1 x 24hr) kW + (25.1 ×5hr) = 7354.3 kWh/day Energy production from biogas For biogas containing 67% of methane: 1 m3 of biogas
6.7 kWh (FNR, 2009)
Assumption:
Density of biogas is 1.18 kg/m3
Efficiency of CHP plant is 40% Amount of biogas going in the CHP = 7566.7 kg/d Flowrate
of
biogas
1 m3 of biogas
𝑚𝑎𝑠𝑠𝑓𝑙𝑜𝑤𝑟𝑎𝑡𝑒 𝑑𝑒𝑛𝑠𝑖𝑡𝑦
=
7566.7 1.18
=
6412.46
m3/d
6.7 kWh
6412.46 m3 of biogas Efficiency
=
(6412.46 x 6.7) = 42963.48 kWh of
CHP
plant
is
40%
Energy obtained from CHP per day = (42963.48 x 0.4) = 17185.39 kWh/d
Page | 115
Appendix C: SIZING Sizing of the MBR Sludge age or sludge retention time As per methodology, the SRT for a membrane bioreactor tank is typically 5 to15 days so as to achieve efficient achieve BOD & nitrogen removal. Therefore, the average SRT is assumed: 𝑆𝑅𝑇 =
5 + 15 = 10 𝑑𝑎𝑦𝑠 2
Feed to microorganism ratio As the biomass is actively removing the organic substrate in the wastewater, it follows that the BOD loading should be related to the volume of the biomass in the aeration tank (i.e. Sludge Loading) Assume F/M ratio for conventional process = 0.2-0.4 𝐴𝑣𝑒𝑟𝑎𝑔𝑒
𝐹 0.2 + 0.4 𝑟𝑎𝑡𝑖𝑜 = = 0.3 𝑚 2
The lower the f/m ratio, the lower the rate of metabolism and the greater the BOD removal and sludge settleability. However, as removal efficiency increases so does the overall oxygen demand of the system and so the overall cost of BOD removal. F/m ratio is also the rate of BOD or COD applied per unit volume of mixed liquor. From Metcalf and Eddy, 2003; F/M ratio can be expressed as: 𝐹 𝑄0 (𝑆0 − 𝑆𝐸 ) = 𝑀 𝑉𝑥 𝑊ℎ𝑒𝑟𝑒𝑏𝑦: F/M = food to microorganism ratio, 𝐾𝑔𝐵𝑂𝐷⁄𝐾𝑑𝑀𝐿𝑆𝑆, 𝑑𝑎𝑦 𝑄0 = Inlet Flowrate, 𝑚3 ⁄𝑑𝑎𝑦 𝑆0 = Inlet 𝐵𝑂𝐷, 𝑚𝑔⁄𝐿 𝑆𝐸 = 𝑂𝑢𝑡𝑙𝑒𝑡𝐵𝑂𝐷, 𝑚𝑔⁄𝐿 X = Reactor solids, 𝑚𝑔⁄𝐿
Page | 116
V = Volume of Aeration tank, 𝑚3 Total aeration volume and dimensions of the MBR tank From the equation of food to microorganism ratio 𝐹 𝑄0 (𝑆0 − 𝑆𝐸 ) = 𝑀 𝑉𝑥 𝑊ℎ𝑒𝑟𝑒𝑏𝑦: F/M =0.3 𝐾𝑔𝐵𝑂𝐷⁄𝐾𝑑𝑀𝐿𝑆𝑆, 𝑑𝑎𝑦 𝑄0 = 70,000 𝑚3 ⁄𝑑𝑎𝑦 𝑆0 = 200𝑚𝑔⁄𝐿 = 14000 kg/day 𝑆𝐸 = Taking into consideration permissible limits, that is 40 mg/L = 2800 kg/day X = Reactor solids, 𝑚𝑔⁄𝐿 Assuming that the bioreactor have a concentration varying in the range 2000 𝑚𝑔⁄𝐿3000𝑚𝑔⁄𝐿 Hence, an average MLSS concentration is calculated which equals to 2500 𝑚𝑔⁄𝐿 V = Volume of Aeration tank, 𝑚3 (𝐾𝑔𝐵𝑂𝐷) 70,000 𝑚3 ⁄𝑑𝑎𝑦 (200 𝑚𝑔⁄𝐿 − 40 𝑚𝑔⁄𝐿) 0.3 = (𝐾𝑑𝑀𝐿𝑆𝑆, 𝑑𝑎𝑦) 𝑉 × 2500 𝑚𝑔⁄𝐿
𝑉 = 14934 𝑚3 From methodology, range of depth should vary from 4m to 7 m Assuming depth 4 m and width 4.4 m typical length to width ratio for MBR Therefore: Width = 4.4 m Length = 44 m 𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝐴𝑟𝑒𝑎 𝑜𝑓 𝑡ℎ𝑒 𝑡𝑎𝑛𝑘 =
14934 𝑚3 = 3733.33 𝑚2 4𝑚
Page | 117
3733.33 𝑚2 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝐶ℎ𝑎𝑛𝑛𝑒𝑙𝑠 = = 19.28 = 20 𝐶ℎ𝑎𝑛𝑛𝑒𝑙𝑠 4.4 𝑚 × 44𝑚 Therefore: Actual Length =
𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝐴𝑟𝑒𝑎 𝐴𝑐𝑡𝑢𝑎𝑙 𝑤𝑖𝑑𝑡ℎ
=
3733.33 4.4×20
= 42.42 𝑚
Dimensions of one channel = 42.5 m × 4.4m ×4.5 m Total surface area of the Aeration tank = 42.5m × (4.4m × 20) = 3740 𝑚2 Dimensions of the tank = 42.5m × 88 m Aeration Period or Hydraulic Retention time 𝑉 𝑚3 14934 𝐻𝑅𝑇 = = = 0.213 𝑑𝑎𝑦 = 5.12 ℎ𝑜𝑢𝑟𝑠 3 𝑄 𝑚 ⁄𝑑𝑎𝑦 70000 Volumetric BOD loadings The volumetric BOD loading is defined as the ratio of BOD (Kg/day to the Volume (m3). 𝑉𝑜𝑙𝑢𝑚𝑒𝑡𝑟𝑖𝑐 𝐵𝑂𝐷 𝐿𝑜𝑎𝑑𝑖𝑛𝑔 =
𝐵𝑂𝐷, 𝐾𝑔/𝑑𝑎𝑦 13,968.5𝐾𝑔/𝑑𝑎𝑦 𝐾𝑔 = = 0.938 3 3 3 𝑉𝑜𝑙𝑢𝑚𝑒, 𝑚 14934 𝑚 𝑚 . 𝑑𝑎𝑦
Oxygen Requirements
Air requirement = 0.8 Kg/ Kg BOD removed Therefore: 𝐴𝑖𝑟 𝑅𝑒𝑞𝑢𝑖𝑟𝑒𝑚𝑒𝑛𝑡 = 0.8 Kg × 11200 Kg/ day = 8960 Kg / day Also since density of air = 1.202 Kg/𝑚3 Air Requirement =
8960 Kg / day = 7454.24 𝑚3 𝑜𝑓 𝑎𝑖𝑟⁄𝑑𝑎𝑦 1.202 Kg/𝑚3
Assuming 21% of oxygen in air; Oxygen Requirement = 7454.24 𝑚3 𝑜𝑓 𝑎𝑖𝑟⁄𝑑𝑎𝑦 × 0.21 = 1565.40 𝑚3 𝑜𝑓 𝑂2 ⁄𝑑𝑎𝑦 Air supplied per 𝑚3 of wastewater treated
Page | 118
7454.24 𝑚3 𝑜𝑓 𝑎𝑖𝑟⁄𝑑𝑎𝑦 𝐴𝑖𝑟𝑠𝑢𝑝𝑝𝑙𝑖𝑒𝑑 = = 0.106 𝑚3 𝑜𝑓𝑎𝑖𝑟⁄𝑚3 𝑤𝑟𝑠𝑡𝑒𝑤𝑎𝑡𝑒𝑟 3 ⁄ 70000 𝑚 𝑑𝑎𝑦 Oxygen supplied per 𝑚3 of wastewater treated 1565.40 𝑚3 𝑜𝑓 𝑂2⁄𝑑𝑎𝑦 𝑂𝑥𝑦𝑔𝑒𝑛𝑠𝑢𝑝𝑝𝑙𝑖𝑒𝑑 = = 0.022 𝑚3 𝑜𝑓𝑂2⁄𝑚3 𝑤𝑎𝑠𝑡𝑒𝑤𝑎𝑡𝑒𝑟 70000 𝑚3 ⁄𝑑𝑎𝑦 Membrane biological reactor Shape
Rectangular
Total volume
14934 m3
Dimensions (L x B x H)
42.5m × 88 m × 4.4 m
Number Of channels
20 channels
Material
reinforced concrete
Water temperature
280C brought to 200C
Liquid depth
7m Fine bubble ceramic diffuser
Aeration system
Oxygen
demand
=
1565.40 𝑚3 𝑜𝑓 𝑂2⁄𝑑𝑎𝑦 Aeration period
5.12 ℎ𝑜𝑢𝑟𝑠
Diffuser submergence
7m
Oxygen transfer efficiency (OTE)
35%
Aeration configuration
Covering the floor completely
Air supply SRT
Using a centrifugal blower feeding 7454.24 𝑚3 𝑜𝑓 𝑎𝑖𝑟⁄𝑑𝑎𝑦 10 days
Page | 119
BOD vol. loading
0.938
F/M
𝐾𝑔 𝑚3 . 𝑑𝑎𝑦
0.3
Appendix D: Costing Purchased Equipment Table Equipment
Quantity
Price US
Price US $
Supplier
$/ unit Screening Shandong Jinhaosanyang mechanical bar screens
2
13943
27886
Environmental Protection Equipment Co.LTD
Oil and Grease trap (APl) Oil and grease separator Centrifugal grit pump
ORGANIC 1
616552
616552
BIOTECH PVT LTD
3
27.13
81.39
Shijazhuang
An
pump Co.LTD
Coagulation and Flocculation Jiangyin Alum tank
dosing
1
1500
1500
Fine
Chemical Machinery Co.LTD
Mixer
1
150
150
Jiangyin
Fine
Chemical
Page | 120
Machinery Co.LTD Rapid mixing tank Flat-Blade Radial
Flow
Turbine
Shaghai 6
120
720
pump
Metal Co. LTD
Impeller Chemical feed
Special
Shijazhuang 1
100.96
100.96
An
Pump CO.LTD
Flocculation Tank Centrifugal pump
6
866.86
5201.16
6
48500
291000
6
903.89
5423.34
4
2000
8000
2
755721.67
1511443.34
Shijazhuang
An
pump Co.ltd Shijazhuang
An
pump Co.ltd Shijazhuang
An
pump Co.ltd
Equalization tank Centrifugal pumps Primary clarifier Reciprocating
An
pump Co.ltd Shijazhuang
An
pump Co.ltd 6
18266.67
109600
pump Centrifuge+
Shijazhuang
Shijazhuang
An
pump Co.ltd 1
617702.60
617702.60
ancillaries
Shijazhuang
An
pump Co.ltd
Heat exchanger Hangzhou Sante
Shell and tube heat exchanger 3 +
200000
600000
Pharmaceutical Chemical
Page | 121
baffles tubing
and +
Equipment
all
Co.,
Ltd.
inlet and outlet piping Hangzhou Sante Pharmaceutical Diesel boiler
1
700000
700000
Chemical Equipment
Co.,
Ltd. Hangzhou Sante Pharmaceutical Gas boiler
1
90000
90000
Chemical Equipment
Co.,
Ltd. Membrane Bio-reactor + Module Membrane Shandong Jinhaosanyang Bio reactor
1
150550
150550
Environmental Protection Equipment
Co.,
Ltd. Shandong Jinhaosanyang Bio digester
1
4000
4000
Environmental Protection Equipment
Co.,
Ltd. Membrane with membranes
1
69750
69750
Microdyne-Nadir
incorporated
Page | 122
Centrifugal pump Chlorination system Centrifugal pump
3
2000
6000
1
104000
104000
4
2000
8000
Shijazhuang
An
pump Co.ltd
Shijazhuang
An
pump Co.ltd
Biogas treatment Dongtai Dongjiang Biogas cooler
1
7000
7000
Shipping Assembly
Co.,
Ltd. Dongtai Reciprocal with inter-cooling
Dongjiang 1
75000
75000
Shipping Assembly
Co.,
Ltd. Packed Tower
1
175000
175000
www.alibaba.com Zhengzhou
Packing materials
-
9000
9000
Macro
Imp.
&
Exp. Co., Ltd. Taian
Flash Tank
1
450000
450000
Luqiang
Metal Vessel CO LTD Taian
Stripping tower 1
300000
300000
Luqiang
Metal Vessel CO LTD
Double membrane gas 4
2000
8000
holder
Page | 123
Taian Absorber
3
100000
300000
Luqiang
Metal Vessel CO LTD
Sand filter Total
valves
and accessories
1
155000
155000
-
1000000
100000
Total Purchase equipment cost Rs:
159268246
Bar screen Price = $7340 – 20546 Taking an average price = $13943 API For a cross sectional area of 20 m², price was $ 105 000 in 2007 For our design, cross sectional area = 60 m², hence price = (105000 × 60)/20 = $ 315000 The cost of the API separator in 2015 can be obtained by the use of the following formula: Cost of equipment A = Cost of equipment B x [(Capacity of equipment A/Capacity of equipment B)]0.6 This equation is applicable for capacity that are increased by a maximum of 10 times the capacity of the old equipment. Hence cost in 2015 = 315000 × (60/20)0.6 = $ 608952 Cost of equipment a = Cost of equipment b × (Capacity of a ÷ Capacity of b)0.6 Rapid Mixing Tank Flat-Blade Radial Flow Turbine Impeller (Ms Rochelle Colardo – Alibaba.com) Price = US $ 120/unit Chemical Feed Pump (Ms Bella Gao – Alibaba.com)
Page | 124
Capacity = 2 L/s Price = US $ 500/unit Cost of chemical feed pump for capacity 0.139 L/s = 500 × (0.139 ÷ 2)0.6 = US $ 100.96/unit Flocculation Tank Horizontal Paddle Wheels Flocculator (Ms Candice Zhu – Alibaba.com) Price = US $ 150/ unit Centrifugal Pump (Ms Tracy Hu – Alibaba.com) Capacity = 792 m3/h Price = US $ 1000/unit Cost of centrifugal pump for capacity 624.17 m3/h = 1000 × (624.17 ÷ 792)0.6 = US $ 866.86/unit Costing Primary clarifiers Theory: Calculating cost of equipment: 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑜𝑓 𝑒𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡 𝑎
Cost of equipment a = cost of equipment b × (𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑜𝑓 𝑒𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡 𝑏)0.6 where, Equipment a: actual equipment Equipment b: equipment used as reference Calculating present cost of equipment: 𝑖𝑛𝑑𝑒𝑥 𝑣𝑎𝑙𝑢𝑒 𝑎𝑡 𝑝𝑟𝑒𝑠𝑒𝑛𝑡 𝑡𝑖𝑚𝑒
Present cost = original cost (𝑖𝑛𝑑𝑒𝑥 𝑣𝑎𝑙𝑢𝑒 𝑎𝑡 𝑡𝑖𝑚𝑒 𝑜𝑟𝑖𝑔𝑖𝑛𝑎𝑙 cost 𝑤𝑎𝑠 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑) Currency: 1 US Dollar = 36.50 MUR
Page | 125
Cost index values1: Year
Cost Index
2007
525.4
2015
767.2 Cost estimation of Primary Clarifiers and Pumps
Equipment and auxiliary
Quantity
Primary circular clarifier
2
Reciprocating pump
6
Primary Clarifiers The cost of the primary clarifier can be calculated using the formula2 below: 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑜𝑓 𝑒𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡 𝑎
Cost of equipment a = cost of equipment b × (𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑜𝑓 𝑒𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡 𝑏)0.6 Capacity of equipments in this context will refer to surface area Now, From Rule Thumb in Engineering Practice3, Cost of equipment b (R.Woods, 2007) = $ 130,000 Surface area of equipment b = 100 m2 Surface area of equipment a = 1000 m2 1000
Cost of equipment a = 130,000 × ( 100 )0.6 = $ 517,539.32 𝑖𝑛𝑑𝑒𝑥 𝑣𝑎𝑙𝑢𝑒 𝑎𝑡 𝑝𝑟𝑒𝑠𝑒𝑛𝑡 𝑡𝑖𝑚𝑒
Present cost = original cost (𝑖𝑛𝑑𝑒𝑥 𝑣𝑎𝑙𝑢𝑒 𝑎𝑡 𝑡𝑖𝑚𝑒 𝑜𝑟𝑖𝑔𝑖𝑛𝑎𝑙 cost 𝑤𝑎𝑠 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑) Original cost in 2007: $ 517,539.32
1
Information retrieved from a pdf online at http://www1.eere.energy.gov/bioenergy/pdfs/mypp_nov_2011_appendix_c.pdf , p.C-11 2 3
Plant Design and Economics for Chemical Engineers, 4th Edition, Peters et al, p.169 Rule Thumb in Engineering, D. Woods, p.408
Page | 126
767.2
Present cost in 2015 = 517,539.32 (525.4) = $755,721.67 Therefore, Present cost in MRU of primary circular clarifier in 2015 = 755,721.67 × 36.50 = Rs 27,583,840.96 Total cost of the 2 clarifiers = 2(27,583,840.96) = Rs 55,167,681.91 Pumps The cost of a reciprocating pump in 2007 was $ 12,500 767.2
Present cost of one pump = 12,500(525.4) = $ 18,266.67 Total present cost of pumps = 6 × 18,266.67 = $ 109,600 Cost estimation of Centrifuge The cost of a centrifuge of with an equivalent clarifying area, Ʃ1, of 2650 m2 had a cost of $ 320,000 in 2007. Thus, the cost of our centrifuge with an equivalent area, Ʃ2, of 2909 m2 is calculated. 2909
Cost of centrifuge = 320,000 × (26500)0.6 = $ 338,416 767.2
Present cost of centrifuge = 338,416(525.4) = $494,162.08 Cost of Ancillaries The cost of the centrifuge and its ancillaries represent a share of 60% and 15% respectively in the capital cost (Directorate General Water Engineering Research and Development Division, n.d.). Hence, 494,162.08
Present cost of ancillaries = 0.15×(
0.6
) = $123,540.52
Cost of centrifuge and ancillaries = 494,162.08 + 123,540.52 = $617,702.60 Summary: Equipment
Primary clarifier
Quantity Unit
2
Cost
Cost($)
equipment($)
755,721.67
1,511,443.34
of
Page | 127
Reciprocating pump
6
18,266.67
109,600
Centrifuge+
1
617,702.60
617,702.60
ancillaries
COMPUTING THE TOTAL CAPITAL INVESTMENT
Total direct cost percentage= 325.5 Total indirect cost percentage = 136 Total direct cost = 0.3255 x PEC = 0.3255 X 159 268 246 = RS 523 196 190
Page | 128
Total indirect cost = 0.136 x PEC = 0.136x 159 268 246 = RS 216 604 815 Fixed capital investment (FCI) = direct cost + indirect cost ∴ FCI = 523 196 190 + 216 604 815 = RS 739 801 005 Working capital (WC) = 0.15 TCI Total capital investment (TCI) = FCI + WC TCI = 739 801 005 + 0.15 TCI ∴ TCI = RS 130 553 119 Calculating the total product cost Total product cost = Manufacturing cost + general expenses 1. Manufacturing cost = Direct Product cost + Fixed charges + Plant overhead Cost A. Direct production costs 1. Raw materials No raw materials are necessary hence the cost for raw materials will be zero. 2. Operating labor Available data: St Martin Treatment plant has an overall plant maximum capacity of 69 000 m3 wastewater/day which is approximately similar to the one designed for a max flow of 75 000 m3/day. Hence the amount of personnel running the plant will be taken similar to that of the St Martin treatment plant. One employee will work 9 hours per day and there will be shift system. Note: the salary of each personnel member is taken from PRB, 2003
Page | 129
Page | 130
Manufacturing cost = Direct production cost +Fixed charges + Plant overhead cost Manufacturing cost = 0.33 TPC + 85115925 Computing the general expenses
TPC = Manufacturing cost + general expenses TPC = 0.33 TPC + 85115925 +0.14 TPC ∴ TPC = Rs 160 596 085
Page | 131
Calculations for depreciation cost The straight line method is used to calculate the overall depreciation of the equipment. The fixed % factor is then evaluated by the double declining method. The depreciation of the equipment over the whole service lifetime is calculated by using the declining balance method. Nevertheless, the yearly depreciation of building is assumed to be a % of the building value. 1. Equipment depreciation Straight line method
Available data: V = 159 268 246 Vs = 30 000 USD (taken reference from St Martin treatment plant) n = 25 (taking in consideration all the equipment)
Double declining balance method,
Page | 132
= 159 268 246 ∴ For 1 year, Vs = 159 268 246 /20 = RS 7963412.32 2. Building depreciation Available data: Building cost from the table above= 1 351 011 USD Depreciation on building = 0.025 x Building cost = 955609 ∴ Total depreciation cost = 7963412.32+955609= RS 8919022 Computing the total income Revenue from sale of treated effluent for irrigation purposes The Wastewater Management Authority sells its treated effluent for irrigation at Rs 0.80/m3 and at the Saint Martin Treatment work the treated water is sold at Rs 0.75/m3. In order to compete with them, the treated water will be sold at Rs 0.50 /m3. Total treated water 73012.95 m3/d Revenue = 0.5x 73012.95x 365= Rs 13 324 863 Sale of sludge cake to composting plant
Page | 133
Typical price of compost on the Mauritian market is Rs 25/kg. Since the waste water treatment plant is providing the compost plant with raw material, the dewatered sludge will be sold at Rs 10/kg. Sludge produced = 72 455 kg per day Total revenue from sludge = 72455 x 10 x 365= Rs264 463 232 Total income = 13 324 863 + 264 463 232= Rs277 788 095 Total profit = Total income – Total product cost ∴ Total profit = 277 788 095 -160 596 085= Rs 117 192 010 Computing the gross profit Gross profit = 117 192 010 – 15 % income tax = 117 192 101 – (0.15x 117 192 101) = 99613209 Computing the payback period
Calculating Rate of Return
Calculating Net Present Value (NPV) The net present value, NPV is defined as the difference between the present value of cash inflows and the present value of cash outflows. The NPV is the most straight
Page | 134
forward way of analyzing the profitability of an investment and is sensitive to the reliability of future cash inflows that an investment or project will yield. The NPV is calculated from:
Where:
Page | 135
NPV = ΣV0 – TCI = 2 163 778 870 – 870 354 123 = 1293424747 Calculating Internal Rate of Return (IRR)
Page | 136
For V0 = 12%, the NPV = ΣV0*Annual cash Inflow - Initial Investment = (7.843*264463232) - 870 354 123 = Rs1203867796 For V0 = 20%, the NPV = ΣV0*Annual cash Inflow - Initial Investment = (4.9475*264463232) - 870 354 123 = Rs438100730.9 For V0 = 25%, the NPV = ΣV0*Annual cash Inflow - Initial Investment = (3.9848*264463232) - 870 354 123 = Rs183502349.6 For V0 = 30%, the NPV = ΣV0*Annual cash Inflow - Initial Investment = (3.3286*264463232) - 870 354 123 = Rs9940702 For V0 = 40%, the NPV = ΣV0*Annual cash Inflow - Initial Investment = (2.499*264463232) - 870 354 123 = Rs -209342970.9 Using extrapolation to find the IRR
∴K= 30.45 IRR = 30.45 %
Page | 137
Discounted Payback Period A capital budgeting procedure used to determine the profitability of a project. In contrast to an NPV analysis, which provides the overall value of a project, a discounted payback period gives the number of years it takes to break even from undertaking the initial expenditure. Future cash flows are considered are discounted to time "zero." This procedure is similar to a payback period; however, the payback period only measure how long it take for the initial cash outflow to be paid back, ignoring the time value of money. Initial Investment = Total Capital Investment = RS 870354123 Assumption: Rate, K = 9 % Discounting Factor = (1+K)-n Where; n = number of years
Discounted payback = 4.079 years
Page | 138
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Detail Design of Wastewater Treatment Plant Research · October 2015 DOI: 10.13140/RG.2.1.3503.4327
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Design Project 2: DESIGN OF A SEWAGE TREATMENT PLANT | keshav soomaree
DESIGN PROJECT 2: DESIGN OF A SEWAGE TREATMENT PLANT
University of Mauritius Faculty of Engineering Department of Chemical and Environmental Engineering 4/3/2015
keshav soomaree 1114132 Coordinator: Mr A.K Ragen Project supervisor: Mr A Mudhoo Student Group: 3A
Table of Contents List of Tables & Figures: ...................................................................................................................... 6 Acknowledgment ................................................................................................................................. 8 List of abbreviations ............................................................................................................................ 8 CHAPTER 1: INTRODUCTION ...................................................................................................... 13 1.1
Aims and Objectives .......................................................................................................... 13
1.2
Summary of starting points for the detailed design ..................................................... 15
Summary of Preliminary mass balances ................................................................................. 15 Summary of preliminary Sizing of equipment ...................................................................... 16 1.3
Description of the wastewater treatment plant’s processes ......................................... 24
Screens ......................................................................................................................................... 24 Oil and Grease Removal............................................................................................................ 24 Equalization Tank ...................................................................................................................... 25 Circular Primary Settling Tank ................................................................................................ 25 The Membrane Bioreactor......................................................................................................... 25 Sand Filter ................................................................................................................................... 26 Chlorination ................................................................................................................................ 26 Thickener ..................................................................................................................................... 26 Sludge Digester .......................................................................................................................... 27 Dewatering Tank ........................................................................................................................ 27 1.4
Process Flow of Proposed Wastewater ........................................................................... 27
1.5
Key findings of the preliminary design .......................................................................... 29
1.6
Job allocation to other members ...................................................................................... 30
CHAPTER 2: Detailed Design .......................................................................................................... 30 2.1
Introduction ........................................................................................................................ 30
2.2
Design Calculations for the MBR ..................................................................................... 33
2.3
Determination of Calculated Parameters ....................................................................... 45
Pressure Calculations ................................................................................................................ 45 Flux Calculation ......................................................................................................................... 46 Temperature Correction ............................................................................................................ 46 Specific Flux ................................................................................................................................ 46 Salt Rejection ............................................................................................................................... 46 Sludge Retention Time .............................................................................................................. 47
Page | 1
Recycle Ratio ............................................................................................................................... 47 2.4
Sizing of the MBR............................................................................................................... 47
2.5
Summary ............................................................................................................................. 49
2.6
Oil-Water separator design............................................................................................... 50
Horizontal Velocity (vH) ............................................................................................................ 52 Minimum Vertical Cross-Sectional Area (Ac) ........................................................................ 52 Channel Width and Depth ........................................................................................................ 53 Separator Length ........................................................................................................................ 53 Minimum Horizontal Area ....................................................................................................... 54 Maintenance ................................................................................................................................ 55 Construction Details .................................................................................................................. 56 Terminal Velocity of Oil Globules in Water ........................................................................... 57 Size and Gravity of Oil Globules ............................................................................................. 59 Derivation of Equation for Separator Length ........................................................................ 59 Calculation and results .............................................................................................................. 60 2.7
PIPE SELECTION AND PIPE SIZING FOR MBR TANKS OUTLETS AND INLETS 63
Pipe Selection .............................................................................................................................. 63 PE (Polyethylene) pipes ............................................................................................................ 64 PVC (Polyvinyl chloride) pipes................................................................................................ 65 Pipe sizing ................................................................................................................................... 65 Calculations................................................................................................................................. 66 2.8
Pump selection for MBR ................................................................................................... 67
2.9
Power requirements for pumps in MBR ......................................................................... 68
Pressure drop in pipelines ........................................................................................................ 69 Miscellaneous pressure losses .................................................................................................. 70 Summary of results .................................................................................................................... 71 CHAPTER 3: Heat and material Balance ........................................................................................ 72 3.1
Material Balance for the MBR........................................................................................... 72
3.2
Energy Balance ................................................................................................................... 77
Heat transfer during cooling .................................................................................................... 77 Analysis of system ..................................................................................................................... 78 Chapter 4:
Mechanical sketches and schedules......................................................................... 79
Chapter 5:
Material of Construction .......................................................................................... 84
Page | 2
5.1
Material of construction for the membrane Bio-reactor Tank ..................................... 84
5.2
Material of construction for the module membrane ..................................................... 84
5.3
Material of construction for the oil-water separator ..................................................... 87
CHAPTER 6: Instrumentation and Control.................................................................................... 89 6.1
Control Strategies for the Membrane Bio-reactor.......................................................... 89
Process control and software .................................................................................................... 89 Pre-treatment and residuals management ............................................................................. 89 Tank sizing and redundancy .................................................................................................... 90 CHAPTER 7: Safety Considerations ................................................................................................ 94 7.1
The oil-water separator ..................................................................................................... 94
7.2
The Membrane Bioreactor................................................................................................. 95
CHAPTER 8: Review of the final design......................................................................................... 95 8.1
Summary of key Deviations ............................................................................................. 95
8.2
Review of API Separator ................................................................................................... 96
8.3
Review of the membrane bioreactor ............................................................................... 96
CHAPTER 9: ECONOMICS OF THE PROJECT, AS DESIGNED ............................................... 98 9.1
Total purchase equipment cost ........................................................................................ 98
9.2
Total capital investment (TCI) .......................................................................................... 98
9.3
Total product cost .............................................................................................................. 99
9.4
Total revenue ...................................................................................................................... 99
9.5
Gross earning cost .............................................................................................................. 99
9.6
Pay-back period ................................................................................................................ 100
9.7
The rate of return ............................................................................................................. 100
9.8
The Net Present Value (NPV) and Initial Rate of Return (IRR)................................. 100
CHAPTER 10: Environmental Concerns..................................................................................... 102 CHAPTER 11: Conclusion............................................................................................................. 103 References ......................................................................................................................................... 104 Appendices ....................................................................................................................................... 108 Appendices A: Mass Balance.......................................................................................................... 108 Mass Balance for the MBR .......................................................................................................... 108 Overall Balance around the MBR .......................................................................................... 108 BOD Balance around MBR ..................................................................................................... 110 Flow Balance ............................................................................................................................. 111 Solid Balance on membrane ................................................................................................... 111
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Balance on VSS on membrane ................................................................................................ 111 NH3-N Balance on the membrane skid ................................................................................. 111 NO3-N Balance on membrane skid........................................................................................ 112 Phosphorus Balance on the membrane skid ........................................................................ 113 Appendix B: Energy Balances ...................................................................................................... 113 Power requirement for the Membrane Bioreactor .................................................................. 113 Energy Balance on Aeration Tank ......................................................................................... 113 Energy Balance on membrane bio filter ................................................................................ 114 Energy balance on the amount of pumps ............................................................................. 115 Energy production from biogas ............................................................................................. 115 Appendix C: SIZING ..................................................................................................................... 116 Sizing of the MBR......................................................................................................................... 116 Sludge age or sludge retention time ...................................................................................... 116 Feed to microorganism ratio................................................................................................... 116 Total aeration volume and dimensions of the MBR tank ................................................... 117 Aeration Period or Hydraulic Retention time...................................................................... 118 Appendix D: Costing ....................................................................................................................... 120 Purchased Equipment Table....................................................................................................... 120 Bar screen ...................................................................................................................................... 124 API.................................................................................................................................................. 124 Rapid Mixing Tank ...................................................................................................................... 124 Flocculation Tank ......................................................................................................................... 125 Primary clarifiers .......................................................................................................................... 125 Calculating cost of equipment:............................................................................................... 125 Calculating present cost of equipment:................................................................................. 125 Cost index values: .................................................................................................................... 126 Cost estimation of Primary Clarifiers and Pumps............................................................... 126 Primary Clarifiers..................................................................................................................... 126 Pumps ........................................................................................................................................ 127 Cost estimation of Centrifuge................................................................................................. 127 Cost of Ancillaries .................................................................................................................... 127 COMPUTING THE TOTAL CAPITAL INVESTMENT ......................................................... 128 Calculating the total product cost .............................................................................................. 129 Computing the general expenses............................................................................................... 131
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Calculations for depreciation cost ............................................................................................. 132 Computing the total income ....................................................................................................... 133 Computing the gross profit ........................................................................................................ 134 Computing the payback period ................................................................................................. 134 Calculating Rate of Return .......................................................................................................... 134 Calculating Net Present Value (NPV) ....................................................................................... 134 Calculating Internal Rate of Return (IRR) ................................................................................ 136 Discounted Payback Period ........................................................................................................ 138
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List of Tables & Figures: 1TABLE 1.2.1: SUMMARY OF MASS BALANCE FOR SEWAGE FLOW OVER THE SYSTEM ........... 15 2TABLE 1.2.2.1: THE OIL-WATER SEPARATOR ........................................................................................ 16 3TABLE 1.2.2.2: BAR SCREEN ........................................................................................................................ 17 4TABLE 1.2.2.3: FINE SCREEN ....................................................................................................................... 18 5TABLE 1.2.2.4: EQUALIZATION TANK ..................................................................................................... 18 6TABLE 1.2.2.5: PRIMARY CLARIFIER ......................................................................................................... 19 7TABLE 1.2.2.6: THE MEMBRANE BIOREACTOR ..................................................................................... 20 8TABLE 1.2.2.7: SAND FILTER ....................................................................................................................... 21 9TABLE 1.2.2.8: CHLORINATION ................................................................................................................. 21 10TABLE 1.2.2.9: THICKENER ........................................................................................................................ 22 11TABLE 1.2.2.10: SLUDGE DIGESTER ......................................................................................................... 22 12TABLE 1.2.2.11: DEWATERING TANK ..................................................................................................... 23 13TABLE 1.5: KEY FINDINGS OF THE PRELIMINARY DESIGN ............................................................ 29 14TABLE 1.6: JOB ALLOCATION OF GROUP MEMBERS ........................................................................ 30 15FIGURE 2.1: EUROPEAN MEMBRANE BIOREACTOR MARKET ....................................................... 31 16TABLE 2.1: BIOLOGICAL OPERATING PARAMETERS ....................................................................... 33 17TABLE 2.2: FEED IN MBR ............................................................................................................................ 39 18TABLE 2.4: KINEMATIC CONSTANTS .................................................................................................... 39 19TABLE 2.5: BIOLOGICAL OPERATING PARAMETERS ....................................................................... 40 20TABLE 2.6: MEMBRANE OPERATING DATA ........................................................................................ 40 21TABLE 2.7: AERATION OPERATING DATA .......................................................................................... 40 22TABLE 2.8: BIOLOGICAL PARAMETERS ................................................................................................ 41 23TABLE 2.9: SLUDGE YIELD ........................................................................................................................ 41 24TABLE 2.10: MEMBRANE CALCULATIONS .......................................................................................... 42 25TABLE 2.11: MEMBRANE OPERATION................................................................................................... 42 26TABLE 2.12: AERATION DESIGN .............................................................................................................. 42 27TABLE 2.13: POWER REQUIREMENT ...................................................................................................... 43 28FIGURE 2.1: SPECIFIC COST VS. FLUX FOR HS AND FS TECHNOLOGIES, FLUX TO BE RELATED TO AERATION DEMAND ...................................................................................................................... 44 29FIGURE 2.3: SPECIFIC COST VS. AERATION DEMAND OVER THE RANGES OF AERATION DEMAND OBSERVED IN PRACTICE FOR HF AND FS TECHNOLOGIES .................................. 44 30FIGURE 2.4: DESIGN VARIABLES FOR OIL INTERCEPTORS. ............................................................ 51 31FIGURE 2.5: RECOMMENDED VALUES OF F FOR VARIOUS VALUES OF VH/VT ...................... 54 32FIGURE 2.6: SKETCH OF PARALLEL PLATE SEPARATOR - CROSS-FLOW ................................... 57 33TABLE 2.14: FLUID DENSITY AND VELOCITY ..................................................................................... 66 34TABLE 2.15: PUMP TYPES AND MAJOR APPLICATIONS IN WASTEWATER TREATMENT ..... 67
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37TABLE 2.17: SUMMARY OF RESULT INVOLVING THE MAIN PIPELINE CONNECTING THE MBR ............................................................................................................................................................ 71 38TABLE 3.1: ENTHALPY OF DIFFERENT GAS COMPONENTS ........................................................... 78 39TABLE 5.2.1: MEMBRANE CONFIGURATION DEFINITIONS ............................................................ 85 40TABLE 5.2.2: MEMBRANE MODULE DETAILS OF FS .......................................................................... 85 41TABLE 5.2.3: MEMBRANE MODULE DETAILS OF HF ......................................................................... 86 42FIGURE 5.3.1: STAINLESS STEEL OIL-WATER SEPARATOR.............................................................. 88 43TABLE 9.0: SUMMARY OF THE ECONOMICS OF THE TREATMENT POWER PLANT ............. 101
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Acknowledgment I wish to thank Mr. Ackmez Mudhoo, our design coordinator, for guiding us and giving us all the possible help that he could. I am thankful to him since he was always present when we needed him and was here to direct us to the right way. I am also grateful to Mr. Arvinda Ragen, our program coordinator, who ensured that we did not lack anything with regards to the project and he did his best to give us all the facilities we needed. I would also like to thank Dr. Dinesh Soorup, the head of department, who responded positively to all the problems faced by us.
List of abbreviations ABR
Anaerobic baffled reactor
Ac
total cross section, m2
AD
Anaerobic digestion
ADUF
Anaerobic digester ultrafiltration
AH
total surface area, m2
Alum
Aluminum [aluminium?] sulphate
AN
Anaerobic
anMBR
Anaerobic membrane bioreactor
AOC
Assimilable organic carbon
ASP
Activated sludge process
AX
Anoxic
B
width of one channel, m
BAC
Biologically activated carbon
BAF
Biological aerated filter
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BNR
Biological nutrient removal
BOD
Biochemical oxygen demand
BPA
Biological potential activity
CEB
Chemically-enhanced backwash
CF
Crossflow
CFV
Crossflow velocity
CIL
Cleaning in line
CIP
Cleaning in place
COD
Chemical oxygen demand
CP
Concentration polarisation
CPR
Chemical phosphorous removal
CST
Capillary suction time
CT
Capillary tube
d
depth of water in channel, m
Da
Dalton
DE
Dead-end (or full flow)
dMBR
Diffusive membrane bioreactor
DO
Dissolved oxygen
DOC
Dissolved organic carbon
DS
Dry solids
EBPR
Enhanced biological phosphate removal
EGSB
Expanded granular sludge bed
eMBR
Extractive membrane bioreactor
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F:M
Ratio Food-to-micro-organism ratio
FBDA
Fine bubble diffusion aeration
FC
Filter cartridge
Flocs
Flocculated particles
FS
Flat sheet (or plate-and-frame)
GAC
Granular activated carbon
GLD
Gigalitres per day
GT
Gas transfer
HF
Hollow fibre
HPSEC
High performance size exclusion chromatography
HRT
Hydraulic retention time
ID
Internal diameter
iMBR
Immersed membrane bioreactor
kDa
kiloDalton
L
length of channel, m
LMH
Litres per m2 per hour
LMH/bar
Litres per m2 per hour per bar
MABR
Membrane aeration bioreactor
ME
Membrane extraction
MF
Microfiltration
MHBR
Membrane hydrogenation bioreactor
MLD
Megalitres per day
MLSS
Mixed liquor suspended solids
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MLVSS
Mixed liquor volatile suspended solids
MPE
Membrane performance enhancer
MT
Multitube
MW
Molecular weight
MWCO
Molecular weight cut-off
n
number of channel
NADH
Nictotinamide adenine dinucleotide hydrogenase
NF
Nanofiltration
NOM
Natural organic matters
O&M
Operation & Maintenance
OC
Organic carbon
OD
Outer diameter
OLR
Organic loading rate
ON
Organic nitrogen
OTR
Oxygen transfer rate
OUE
Oxygen utilisation efficiency
p.e.
Population equivalent
PAC
Powdered activated carbon
PAN
Polyacrylonitrile
PE
Polyethylene
PES
Polyethylsulphone
PP
Polypropylene
PV
Pervaporation
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PVDF
Polyvinylidene difluoride
Qm
Flow of oily water into the oil-water separator, m3/s
RBC
Rotating biological contactor
Rc
Cake resistance
Redox
Reduction-oxidation
rMBR
(Biomass) rejection membrane bioreactor
RO
Reverse osmosis
SAD
Specific aeration demand
SADm
Specific aeration demand – membrane area
SADp
Specific aeration demand – permeate volume
SAE
Standard aeration efficiency (kgO2/kWh)
SBR
Sequencing batch reactor
SCADA
Supervisory control and data acquisitions
SDI
Silt density index
sMBR
Sidestream membrane bioreactor
SMP
Soluble microbial product
SMPc
Soluble microbial product (carbohydrate)
SMPp
Soluble microbial product (protein)
SNdN
Simultaneous nitrification/denitirification
SRF
Specific resistance to filtration
SRT
Solids retention time
SVI
Sludge volume index
SW
Spiral-wound
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TDS
Total dissolved solids
TF
Trickling filter
THMFP
Tri-halo methane formation potential
TKN
Total Kjedldahl nitrogen
TMDL
Total maximum daily load
TMP
Transmembrane pressure
TOC
Total organic carbon
TSS
Total suspended solids
UF
Ultrafiltration
VH
horizontal flow velocity, m/s
VRM
Vacuum rotating membrane
VSS
Volatile suspended solids
Vt
rise rate of oil globule, m/s
WRP
Water recycling (or reclamation) plant
WWTP
Wastewater treatment plant
CHAPTER 1: INTRODUCTION Sewage is a major carrier of disease and toxins .The safe treatment of sewage is thus crucial to the health of any community. This Project focuses on the complex physical and biological treatments used to render sewage both biologically and chemically harmless. 1.1
Aims and Objectives
The design project consists of two parts namely a ‘Preliminary report’ (Design Project 1) and a ‘Detailed report’ (Design Project 2). This detailed design is a follow up of the previous preliminary design conducted and it deals with the review of all the limitations of the design 1. The results obtained previously are fine-tuned and
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mechanical designs of the major equipment are prepared. In Mauritius, rapid population growth and unplanned development are contributing to rapid depletion of per capita water availability. Moreover, a limited amount of rainfalls accompanied with a high rate of evaporation and redundant habit of wasting water of the population; even though severe dry season prevailing are the breeding factors for water shortage. Similarly, with an annual swell of 3% in the volume of water injected into the distribution system during the past 20 years, has shot the daily water consumption per capita from 152 liters in 1990 to 216 liters in 2013(Digest of Energy and Water Statistics, 2013) and many are convinced that we are just a few drops away from the “Water Scarce” status. Thus, there was an urgent need for a strategic plan that tackle this issue. Likewise, more emphasis is being laid on preservation and protection of environment while the government came forward with an excellent strategic plan; National Sewerage Project (NSP, 2011), set up to solve at one go the water scarce. Opting for wastewater treatment ensures that not much great demands are been made on the environment in Mauritius, therefore it is a step forward towards safeguarding the ecological and marine resources, in particular surf water and ground water and as well as improve sanitation and protect public health. In addition, the opting for wastewater treatment and reuse makes provision for long term water reliability within the community by providing substitute for fresh water and also is a plus-point for water demand and drought management in overall water resources planning. Likewise, reuse of wastewater also enables the allocation of good quality fresh surface water or ground water for higher value purposes, which can be either for human consumption or meeting domestic needs, thus also protecting existing sources of fresh water as it obviate the requirement of mobilization of additional resources to increasing demand. On the other hand, one of the aims of this project is to study the feasibility of implementing a wastewater treatment plant for an industrial wastewater possessing certain specified characteristics and simultaneously device certain processing strategies that will enable compliance of the treated water with the irrigation norms.
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The objective of the detailed design project is intended to bring together the knowledge and skills that have been assimilated through the B Eng. (Hons) Chemical & Environmental Engineering undergraduate course and to demonstrate creative and critical powers in making decisions in areas of uncertainty. 1.2
Summary of starting points for the detailed design
The Detailed Design Project will be started based upon values of the preliminary design. The limitations which are revised in this report are also listed. Summary of Preliminary mass balances 1Table 1.2.1: Summary of mass balance for sewage flow over the system
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Table 1.2.1(continued)
Summary of preliminary Sizing of equipment 1.2.1.1 The Oil-Water Separator 2Table 1.2.2.1: The oil-water separator
Vertical Velocity
0.18083 cm/s
Horizontal flow velocity
1.5 cm/s
minimum vertical cross-sectional area
54 m2
number of channels
2
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Width of channel
8m
Depth of channel
3.38 m
Length of channel
3.33 m
Limitation: The system was designed assuming that only free oil is present in the effluent, other types of oil may be present which may affect the efficiency of the system. 1.2.1.2 Bar Screen 3Table 1.2.2.2: Bar screen
Depth of chamber, d
1.50 m
Total width of opening at the rack, w
0.6m
Clear bar spacing
50 mm
Number of bars
12
Width of bar
10 mm
Thickness of bar
50 mm
Width, W of the chamber
0.72 m
Height of rack( allowing 0.6 m of freeboard)
2.0 m
Angle of inclination of the bars to the horizontal, θ
80˚
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1.2.1.3 Fine screen 4Table 1.2.2.3: Fine screen
Depth of chamber, d
2m
Total width of opening at the rack, w 0.45 m
Clear bar spacing
9.5 mm
Number of bars
48
Width of bar
10 mm
Thickness of bar
50 mm
Width, W of the chamber
0.93 m
Height of rack( allowing 0.6 m of freeboard) Angle of inclination of the bars to the horizontal, θ
2.63 m
80˚ Mainly of stainless steel for protection
Material of construction
against corrosion and for higher lifetime
1.2.1.4 Equalization Tank 5Table 1.2.2.4: Equalization Tank
Number of Equalization tank
3
Flow rate per tank, Q (m3/h)
967.87 m3/h
Retention time (hours)
3 hours
Area (m2)
556.42 m2
Volume (m3)
3,338.52 m3
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Length (m)
33.36 m
Breadth (m)
16.68 m
Freeboard (m)
0.5 m
Inlet velocity (m/h)
1.73 m/h
Material of construction
Concrete
Limitations: 1. The effluent was assumed to have an overall constant mass loading which is practically impossible in reality. 2. The tank was assumed to be constant volume basin, again since no interior slope was provided it is impossible to be achieved. 3. The assumptions and calculations yield a large volume of equalization tank which is may not be required. 1.2.1.5 Primary Clarifier 6Table 1.2.2.5: Primary Clarifier
Number of tank
2 clarifiers in parallel
Flow rate per tank, Q (m3/h)
1458.3
Retention time (hours)
2.5
Area (m2)
1000
Volume (m3)
3646
Tank Diameter (m)
36
Height (m)
3.65
Material of construction
Concrete
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1.2.1.6 The Membrane Bioreactor 7Table 1.2.2.6: The membrane Bioreactor
Shape
Rectangular
Total volume
14934 m3
Dimensions (L x B x H)
42.5m × 88 m × 4.4 m
Number Of channels
20 channels
Material
reinforced concrete
Water temperature
28 0C brought to 20 0C
Liquid depth
7m Fine bubble ceramic diffuser
Aeration system
Oxygen
demand
=
1565.40 𝑚3 𝑜𝑓 𝑂2⁄𝑑𝑎𝑦 Aeration period
5.12 ℎ𝑜𝑢𝑟𝑠
Diffuser submergence
7m
Oxygen transfer efficiency (OTE)
35%
Aeration configuration
Covering the floor completely Using a centrifugal blower
Air supply
feeding 7454.24 𝑚3 𝑜𝑓 𝑎𝑖𝑟⁄𝑑𝑎𝑦
SRT
10 days
BOD vol. loading F/M
0.938
𝐾𝑔 𝑚3 . 𝑑𝑎𝑦
0.3
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1.2.1.7 Sand Filter 8Table 1.2.2.7: Sand Filter
Number of sand filter
1
Flow rate/ sand filter, Q (m3/h)
69,674 m3/day
Area (m2)
87.5 m2
Breadth (m)
9.35 m
Length (m)
9.35 m
Volume (m3)
305.98 m3
Under drain depth (m)
0.8 m
Filtration duration (h)
20 hours (per day) Reinforced concrete is used
Material of construction
for the tank with the filter media being sand.
1.2.1.8 Chlorination 9Table 1.2.2.8: Chlorination
Number of tank
4
Flow rate of NaOCl /channel, Q
0.00564 m3/s
Volume of 1 tank
362.9 m3
Volume of 4 tanks
1,451.5 m3
Depth
1.8 m
Breadth
2.2m
Cross sectional area
3.96 m2
Length
91.6 m
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Length of each channel
30.5 m
1.2.1.9 Thickener 10Table 1.2.2.9: Thickener
Number of thickeners
2
Volume (m3)
956.12 m3
Surface area (m2)
152.59m2
Diameter (m)
13.94 m
Side water depth (m)
5.8 m
Depth at central hopper (m)
7.19 m
Thickening period (days)
3.48 days
Total flow (m3/d)
548.94 m3/d Reinforced concrete for tank while inner
Material for construction
equipment are of stainless steel, resistant to corrosion
1.2.1.10 Sludge Digester 11Table 1.2.2.10: Sludge Digester
Number of digesters
2
Volume (m3)
2019.6 m3
Area (m2)
176.71m2
Diameter (m)
15 m
Side wall height (m)
13.22 m
Central hopper depth (m)
14.72 m
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Amount of VSS in thickened sludge (Kg /d)
13511.96 Kg/d Reinforced concrete is used for the digesters
Material for construction
while
any
other
equipment is made up of stainless steel.
1.2.1.11 Dewatering Tank 12Table 1.2.2.11: Dewatering Tank
FIRST TANK Number of tank
1
Surface area
1.85 m2
Volume designed
1.92 m x 0.96 m x 1m + 0.5m (freeboard)
Total solids flowrate
763 kg/hr
total amount of polymer used Material for construction
2.771 kg/hr Fiber glass is used. Inox stainless steel is chosen the stirrer.
MATURATION TANK Number of tank
1
Volume designed
1.85m3
Surface area
1.85 m2
Flow
rate
solution
of
polymer
17.08 m3 /hr
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Material for construction
1.3
Fiber glass is used. Inox stainless steel is chosen the stirrer
Description of the wastewater treatment plant’s processes
Industrial wastewater treatment encloses various mechanisms and processes used to treat water that have been contaminated in some way by anthropogenic industrial or commercial activities prior to its release into the environment or its re-use. Similar the mechanisms or processes to be employed to treat the water is chiefly dependent on the characteristics of the water and depend on the subsequent possible reuse of the water. Thus the treatment facility has designed to treat the effluent to comply with the irrigation norms and in subsequent text below provide an overview of different system employed. Screens A screen is a device with openings, generally of uniform size, that is used to retain solids found in effluent wastewater (Metcalf and Eddy, 2004) and often the first unit operation in wastewater treatment plant. Basically screens can be classified by two methods; firstly by their method of cleaning: hand cleaned or mechanically cleaned and secondly by the size of their clear openings: coarse, medium and fine screens. Likewise in our case, the wastewater will pass through a climber type mechanically raked screen for the removal of coarse screens since the designed flow-rate is considerably large. Oil and Grease Removal To start with, a simple assumption that was prompted while considering the design of the oil and grease separator; is that the total oil and grease concentration was due to the presence of free oil. The latter is in the form of discrete globules with size sufficient enough for its globules to rise as a result of buoyant forces forming an oil layer at the water surface. Free oil can be removed under proper quiescent conditions by gravity method. Thus in the case of our design we will go for the API gravity separator due to the fact that it has been successfully been used in refineries for many years (Kirby S. Mohr 2001). The basic design of an oil water separator is a long
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rectangular basin with a detention time of about 30 minutes (Metcalf and Eddy, 2004) with an efficiency of 92%. Most of these separators are divided into more than one bay and are usually equipped with scrapers to move the oil downstream where it is collected on a drum. The sludge produced can be dewatered, incinerated or disposed of in hazardous waste landfills. Equalization Tank In the preliminary design, assuming that the wastewater has an overall constant mass loading; and in line equalization tank was considered despite its constraints like larger volume requirement and higher operational cost due to continuous pumping of wastewater from the equalization since it offers a more uniform flow and strength of wastewater. Since the tank was placed just after the PST and with a short detention time so neither no mixing or aeration processes was provided as a control measure to avoid deposit solids or odor formation. Circular Primary Settling Tank Prior to the settling tank, there are the flocculation tanks and mixing tanks that will allow for the formation of flocks that will trap both the total suspended solids and the organic matter as biochemical oxygen demand present in the wastewater. This technique is referred as advanced sedimentation process and the mostly applied flocculent is alum. The settling tank can remove up to 80% of total suspended solids and 40% of the biochemical oxygen demand. A circular setting was selected since this allows for central feeding of wastewater to the top of the tank, therefore increasing favoring better settling of the flocks formerly produced. Sludge will be collected at the bottom of the tank and will be used, mixed with sludge from other units of the plant for the production of biogas. The Membrane Bioreactor There are essentially three main elements of a membrane bioreactor (MBR) contributing to operating costs, ignoring membrane replacement. These are: 1. Liquid pumping 2. Membrane maintenance 3. Aeration
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Of these by far the most significant, especially for immersed technologies, is aeration. As already discussed in the primary design, aeration is used both for scouring an immersed membrane and for suspending and maintaining a viable biomass. Design of an MBR therefore demands knowledge both of the feed water quality, which principally determines the oxygen demand for bio-treatment, and the aeration demand for fouling control, which relates to a number system characteristics. Sand Filter Slow sand filters proved to be uneconomical when compared to rapid sand filters and micro screen where the efficiency reached were about 60 % for suspended solids (TSS) and about 40 % for BOD. Operation of a rapid sand filter consists of regular backwashing. The period between backwashes depends on the quality of the water being filtered. The purpose of backwashing is to remove the suspended material that has been deposited in the filter bed during the filtration cycle. Periodic repacking of the filter bed may be required at infrequent intervals to ensure efficient operation (Negulescu, 2011). Rapid sand filter are preferred compared to slow filter as back washing occurs rapidly and it has a high filtration rate of about 150 to 200 million gallons of water per acre per day. Chlorination The most frequent disinfectants are chlorine, ozone and UV rays UV rays, being highly effective for pathogen sterilization, are also very expensive. Ozone is highly toxic but not readily available. Considering the effects and inconveniences of UV rays and ozone, Chlorination is chosen, even though it is somehow toxic as it increases the total dissolved solids in the effluent, it is the less expensive one (Hung et al. 2012). It must be noted that due to the selection of the membrane bioreactor in our system, which has a very high initial cost, we need to minimize the cost for our other units. Thickener Gravity thickener is the most common type of thickener which can act as a thickener and achieve blending, important to produce a uniform mixture for subsequent processes at the same; thereby eliminating the need for a separate blend tank. This type of thickener is chosen since the solids concentration of 4 – 6 % achieved by a
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gravity thickener that is required by the high rate digester. It requires the minimum power consumption compared to dissolved air flotation and centrifugal thickener. It also has the least operation skill requirement and operating costs. Conditioning chemicals and polymer are typically not needed as is the case for gravity belt thickener and rotary drum thickener. The pH can also be adjusted in this type of thickener which can provide space for storage (Metcalf and Eddy, 2003). Sludge Digester High rate digestion is deemed suitable for the process as it requires less space and short detention time of 10 – 30 days compared to low rate digestion. Mesophilic digestion is chosen since the operating temperature for these organisms is 30 – 38 0C; thus reducing less energy requirement compared to the thermophilic digestion where fluctuations in temperature can cause process instability and a risk of higher odor potential. Thermophilic and 2 stage digestion process produce a poorer quality supernatant which contains dissolved materials; requiring further special treatment. As for the 2-stage digestion process, it is still under pilot studies and will be more energy intensive; requiring 2 mixing devices for both tanks. Dewatering Tank The aim of the dewatering equipment is to achieve fifty percent by dry weight solids content and centrifuge equipment can produce the required percent. In addition, its capital cost is low when compared to other methods, there is minimization of odor as it is an enclosed unit and requires little supervision; thus continuous solid bowl centrifuge is chosen since it is more suited for high solid content and used for medium and large plants compared to imperforated basket centrifuge. Filter press has many inconveniences such as mechanical complexity; high chemical and labor costs and limitation on filter cloth life while vacuum filtration has low operational costs but higher initial costs and land requirements. 1.4
Process Flow of Proposed Wastewater
Next is the process flow diagram of proposed wastewater treatment
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BS1:1st Bar Screen BS2:2nd Bar Screen RS: Raw Sewage PS: Primary Sludge
PC1: 1st Primary Clarifier PC2: 2nd Primary Clarifier GT: Gravity Thickener SD: Sludge Digester
CS: Clear Supernatant S: Screenings OGT: Oil & grease Trap AB: Air Blower
ET: Equalization Tank CD: Centrifuge Dewatering SF: Sand Filter EP: Electricity to Plant
BT: Bioreactor Tank MS: Membrane Skid LT: Landfill Truck CU: Chlorination Unit
TT: Transportation Truck WAS: Waste Activated Sludge EI: Effluent to Irrigation OG: Oil & Grease
AB
PC1
BT
BS1
MS
ET SF PC2
BS2 OGT PS
S OG
CS LT
WAS GT
FLOWLINE ANNOTATIONS Raw Sludge
Biogas
Oil & Grease
Electicity
Screenings
Filtered Effluent
Sewage
Air
Air Clear Supernatant
SD
EP
EG
Disinfected Effluent
Chlorine
CS
CD TT
Primary Sludge Waste Activated Sludge
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1.5
Key findings of the preliminary design
13Table 1.5: Key findings of the preliminary design
Equipment Coarse 1
screens
(Inclined
QTY
Cost ( Rs) / unit
Total Cost / Rs
2
253,150
506,300
2
305,000
610,000
1
300,212.17
300,212
bar
screen with rack and pinion system- Infilco Degremont bar screen)
2
3
Fine bar screen (Fine straight bar screen GFD type) Rectangular in-line equalization tank equipped with mixer
4
Circular clarifier
2
23,082,825.07
46,165,650
5
MBR
1
3,536,920
3,536,920
1
226,441.24
226,441
1
40,371,838.51
40,371,839
1
6,955,415.34
6,955,415
6 7 8
Rapid Sand Filtration equipped with an inlet chamber Thickener Square
Based
UASB
digester
sludge
9
Centrifuge
1
2,003,400
2,003,400
10
Pumps
9
61,500
553,500
11
Oil separator
1
15,762,107.85
15,762,108
Total Purchase Equipment Cost
116,991,785
Net income = Rs 25,611,771.6 Payback period = 7 years
Page | 29
1.6
Job allocation to other members
14Table 1.6: Job allocation of group members
Wastewater Treatment – Group 3A Name
Equipment Allocated
RAMDHONEE A.K.R. Mishra
Gravity Thickener & Equalization Tank
SOOMAREE Keshav
Membrane Bioreactor(Major) & Oil-Water Separator(Minor)
RAMANAH R. Devi (Ms)
Sludge digester & Sand filter
ST PAUL M.M. Eldora (Ms)
Clarifier & dewatering unit
RAMDEWAR P. Kumar
Screening & Disinfection unit (Chlorination)
CHAPTER 2: Detailed Design Major: Design of the Aerobic Membrane Bioreactor. 2.1
Introduction
The progress of technological development and market penetration of membrane bioreactors (MBRs) can be viewed in the context of key drivers, historical development and future prospects. As a relatively new technology, MBRs have often been disregarded in the past in favor of conventional bio treatment plants. However, a number of indicators suggest that MBRs are now being accepted increasingly as the technology of choice. Market analyst reports indicate that the MBR market is currently experiencing accelerated growth, and that this growth is expected to be sustained over the next decade. The global market doubled over a 5-year period from 2000 to reach a market value of $217 million in 2005, this from a value of around $10 million in 1995. It is expected to reach $360 million in 2015 (Hanft, 2006). As such, this segment is growing faster than the larger market for advanced wastewater treatment equipment and more rapidly than the markets for other types of membrane systems. In Europe, the total MBR market for industrial and municipal users was estimated to have been worth €25.3 million in 1999 and €32.8 million in 2002 (Frost and Sullivan,
Page | 30
2003). In 2004, the European MBR market was valued at $57 million (Frost and Sullivan, 2005). Market projections for the future indicate that the 2004 figure is expected to rise annually by 6.7%; the European MBR market is set to more than double its size over the next 7 years (Frost and Sullivan, 2005), and is currently roughly evenly split between UK/Ireland, Germany, France, Italy, the Benelux nations and Iberia (figure 1.1) The future for the MBR market is thus generally perceived to be optimistic with, it is argued, substantial potential for growth. This level of optimism is reinforced by an understanding of the key influences driving the MBR market today and those which are expected to exert an even greater influence in the future. These key market drivers include greater legislative requirements regarding water quality, increased funding and incentives allied with decreasing costs and a growing confidence in the performance of the technology. 15Figure 2.1: European membrane bioreactor market
(Frost and Sullivan, 2005)
MBR Market 16%
19%
UK and Ireland Germany
19% 18% 16%
12%
France Italy Iberia Benelux
It appears to be true that traditionally decision-makers have been reluctant to invest the relatively high start-up costs required on a relatively new technology (15 years) which produces an output of higher quality than that required. This is especially so
Page | 31
when MBRs have historically been perceived as requiring a high degree of skill and investment in terms of operation and maintenance (O&M) with key operating expenditure parameters, namely membrane life, being unknown (Frost and Sullivan, 2003). Whilst robust to changes in loading with respect to product water quality, MBR O&M protocols are critically sensitive to such parameters because of their impact on the membrane hydraulics (i.e. the relationship between throughput and applied pressure). Whilst there are many examples of the successful application of MBRs for a number of duties, there are also some instances where unscheduled remedial measures have had to be instigated due to under-specification, inappropriate O&M and other factors generally attributable to inexperience or lack of knowledge. All of this has fed the perception that MBRs can be difficult to maintain. In the past there have been an insufficient number of established reference sites to convince decision-makers of the potential of MBRs and the fact that they can present an attractively reliable and relatively cost effective option. This is less true today, since there are a number of examples where MBRs have been successfully implemented across a range of applications, including municipal and industrial duties. In many cases the technology has demonstrated sustained performance over the course of several years with reliable product water quality which can, in some cases, provide a clear cost benefit. Lastly, developing new water technology, from the initial laboratory research stage to full implementation, is costly and time consuming (ECRD, 2006). This problem is particularly relevant considering that the great majority of water technology providers in Europe are small- and medium-sized enterprises (SMEs) that do not have the financial resources to sustain the extended periods from conception at laboratory scale to significant market penetration. Whilst the most significant barrier to the more widespread installation of MBRs remains cost, there are a number of drivers which mitigate this factor. Foremost of these is increasingly stringent environmental legislation relating to freshwater conservation and pollution abatement which has driven technological development in the water sector over the last 30–40 years. This, along with various governmental,
Page | 32
institutional and organizational incentives, has encouraged problem holders to appraise more sophisticated technologies such as MBRs in recent years. Moreover, both capital (and particularly membrane) and operational costs of the MBR process have decreased dramatically over the past 15 years, although further significant cost reductions may be unattainable unless membrane modules become standardized in the same way as has taken place for RO technologies. 2.2
Design Calculations for the MBR
16Table 2.1: Biological operating parameters
Raw data
Calculated data
Average
flow
(m3/day)
Q
specific
substrate Utilization µm/Y rate (kg/(g/day))
Peak
flow
(m3/day) BOD
Maximum
influent
(mg/L)
Qpeak
Effluent BOD (Sg/m3) Ks(1-Keθx)/ θx(YK-Ke)-1 Specific
S0
growth
of
nitrifying
1/θx
bacteria, µng/(g/day)
Biodegradable COD
(mg/L)
(often taken a 1.6
bCOD
Effluent nitrogen (Ne g/m3)
Kn(µn+Ke,n)/µn,m- Ke,n-µn
BOD) Total
suspended
solids
influent TSS
Cell debris ( fd g/g)
≈ VSS/S0
(mg/L) TSS
effluent
(mg/L) (normally TSSe negligible) Volatile suspended solids (mg/L)
VSS
Sludge
yield
(Px
g/day) Non-biodegradable solids (X0 g/day)
[QY(So-S)/(1+ Keθx)] – [fdKeQY θx(So-S)/
(1+
Keθx)]
[QYnNOx/(1+ Ke,nθx)] (TSS -VSS)Q
Page | 33
–
Wastewater
Tw
temperature (°C)
Sludge wastage flow (Qw m3/day) Observed yield, Yobs
SRT (day)
θx
mg VSS/(mg BOD day)
Design
mixed
liquor suspended MLSS solids (mg/L) Anoxic
tank
V m3 Food
as
percentage
Aerobic tank volume
of Va /Van
aerobic tank size
to
[Y/(1+ ke θx)] + [fd Ke Y θx/(1+ ke θx)]
Px θx/X
micro-
organisms ratio, F:M kg
V/ θx
BOD/(kg
SQ/VX
TSS/day)
Maximum specific growth
rate
(heterotrophic) (mg
µm
VSS/(mg
Oxygen requirement, Q [(So-S) - 1.42Px/Q + 4.33 NOxm0 kg/day
2.83NOx
VSS/day)) Saturation coefficient (heterotrophic)
Required airflow to Ks
(mg/L BOD)
meet
biological
requirements,
QA’,b
(RoXOTE)/(ρA0.21αβτ)
kg/day
Endogenous decay coefficient (heterotrophic), (mg
Ke
α factor
e-0.084.X
VSS/(mg
VSS/day) Yield
coefficient
(heterotrophic) (mg VSS/(mg BOD
Y
Sludge wastage, Qw m3/day
V/ θx
Page | 34
Maximum specific growth
rate
Sludge waste per unit
(nitrification), (mg µm,n
permeate
QW/J’netAm
VSS/(mg
(Qw,vm3/(m3day)
VSS/day)) Endogenous decay coefficient
Airflow
per
(nitrification) (mg Ke,n
permeate
VSS/(mg
m3/(m3/day))
unit (Rb QA,B/ ρA J’netAm
VSS/day)) Yield
coefficient
(nitrification), mg Yn VSS/(mg BOD)
Normalized
Raw data
or
derived
data
Mean flux (LMH)
J
Mean
Temperature-corrected
J/1.024 (T-20)
flux, J’, LMH Temperature-corrected
transmembrane
∆Pm
pressure (bar)
mean
permeability J’/∆Pm
(LMH/bar) Temperature,
Aeration rate (m3/h)
QA,m
corrected
pressure-
aeration
rate,
Q’A,m (m3/h) Temperature wastewater (K)
of
TW,K
Temperature-corrected net flux, J’net (LMH)
QA,m(293/
Ta,K)*(
Pa.l/101.323)
N[(J’ tb – J’ τb)/( tc + τc)
Page | 35
Membrane Inlet air temperature (K)
Ta,K
aeration
demand
per
membrane
area,
unit SADm
Q’A.m/A’m
(Nm3/(hm2)) Inlet
air
pressure
(kPa)
Membrane Pa.l
aeration
demand per unit permeate Q’A.m/J’Am flow, SADp Specific membrane aeration
Membrane area (m2)
Am
energy
demand,
Wb,V KQ’A.m/ ρaJ’Am
(kWh/m3) Physical
Specific hydraulic energy
cleaning(backflush)
tb
interval (h)
demand
for
membrane ∆P/ ρp
permeation, Wh (kWh/m3) Specific
Physical cleaning(backflush)
τb
duration (h)
recirculation
energy demand per unit permeate
volume,
Wp
RρbgH/1000 ξ
(kWh/m3) Mass of chemical reagent
Backflush flux (LMH) Jb
per unit permeate volume, cc vc/ J’net Am( tc + τc) Mc (kg/m3)
Cleaning interval (h)
tc
Cleaning duration (h) τc Cleaning
reagent
strength (kg/m3) Cleaning
reagent
volume (m3)
cc
vc
Density (kg/m3)
ρ
Pumping efficiency
ξ
Conversion
According to Metcalfe and Eddy (2003), pp. 709.
Page | 36
Sizing of the MBR Packing density given by ratio of fibre surface area to volume Φ = Af / V
Where
(1)
Af = surface area of fibres = Nπdf
(2)
V = module volume Av = volume occupied by fibres = Nπdf 2/4
(3)
So: Av/ Af = df / 4
(4)
Thus; Ax = (4V – df Af) / 4L
(5)
Where Ax = free x-sectional area So: QA = 3600U / 4L x (4V - – df Af)
(6)
Where QA = aeration rate in m3/hr U = air flow velocity in channels (m/s) SADm = 3600U / 4V x (4V/Af – df)
(7)
Where SADm = aeration demand with respect to fibre area Substituting for V/Af and normalizing against flux: SADp = 3.6x106U / 4LJ x (4/ Φ – df)
(8)
Where SADp = aeration demand with respect to permeate volume Evidence suggests that J is a linear function of aeration intensity: J = mU + c
(9)
Where m and c are empirical constants So: SADp = 3.6x106U / 4L (mU + c) x (4/ Φ – df)
(10)
Aeration energy demand in kWh/m3 permeate is then given by
Page | 37
EA = 0.0303 SADp γ x [((10x + 101) / 101)(1 – 1/ γ) – 1] / (γ – 1) ζ (11) Where γ = aerator constant = 1.4 ζ = blower efficiency = 0.5 x = aerator depth = 3 m So: EA = Uk / L (mU + c) x (4/ Φ – df)
(12)
Where K = 0.0303 x 3.6x106 / 4 x γ x [((10x + 101) / 101) (1 – 1/
γ)
– 1] / (γ – 1) ζ and is thus
constant for a given system. Now, commercial technical data for available membrane modules (Judd, 2006) suggests that, for packing density and fiber diameter respectively in m-1 and m: 1 / Φ ≈ gdf + 0.001 f
(13)
Where f = 0.7-1.7 and g = 0.9-1.1 Thus EA = Uk / L (mU + c) x [(4/g-1) df + 0.004f)
(14)
For the four main MBR HF membrane suppliers, g = 0.89 (R2 = 0.97) and f = 1.7, and thus: EA = Uk / L (mU + c) x [3.5 df + 0.0068]
(15)
Design calculation A complete design for an immersed membrane bioreactor (iMBR) can be carried out on the basis of the information presented, provided the nature of the interrelationship can be determined between aeration and: (a) Permeability and cleaning protocol for the membrane permeation component,
Page | 38
(b) Feed water quality, flows and bio kinetics for the biological component. 17Table 2.2: Feed in MBR
Parameter
Value
Units
Q
50,000
m3/day
Qp
203384
L/H
Qpeak
1000
L/H
BOD So
220
g/m3
COD
430
g/m3
BOD:COD ratio
1:2
TSS
250
g/m3
VSS
190
g/m3
N
40
g/m3
Non-biodegradable VSS
0.24
g/gTSS
TW
12
oC
TW,K
285
oK
Ta
15
oC
Ta,K
288
oK
Pa,I
101
kPa
ρa
1.23
Kg/m3
ρb
1003
Kg/m3
ρp
996
Kg/m3
18Table 2.4: Kinematic constants
BOD Parameter
Ammonia Values
Unit
Parameter
Values
Unit
Ks
60
g/m3
µm,n
0.41
g/(g/day)
Ke
0.06
Per day
Kn
0.05
g/m3
Y
0.4
g/gBOD
Kdn
0.07
g/(g/day)
T = 20 oC
Page | 39
µmax
4.7
g/(gVSS/day) Yn
0.13
g/(g/day)
fd
0.86
gnbSS/gfeed
0.040
g/(g/day)
Yobs
0.64
g/gBOD
µn
According to Metcalfe and Eddy (2003), pp. 709. 19Table 2.5: Biological Operating Parameters
Parameter
Values
Unit
X
8000
g/m3
θx
25
day
Van/V
0.3
r
2
20Table 2.6: Membrane Operating Data
Parameter
Values
Unit
K
100
LMH/bar
J
25
LMH
tb
0.167
h
τb
0.013
h
Jb
35
LMH
n
938
∆Pm
0.25
bar
SADm
0.92
m3/(m2h)
tc
168
h
τc
2
h
cc
0.25
kg/m3
JCIP
45
LMH
21Table 2.7: Aeration Operating Data
Parameter
Biology
Membrane
Diffuser type
Fine bubble
Coarse bubble
Page | 40
OTE per m
0.05
0.02
α
-
0.49
β
-
0.95
Φ
-
0.89
Parameter
Values
Unit
V
2980
m3
Van
894
m3
Se
0.81
g/m3
Ne
0.018
g/m3
Ro
1395
Kg/day
Aerobic HRT(average)
14.3
h
Aerobic HRT(peak)
3
h
Anoxic HRT(average)
4.3
h
Anoxic HRT(peak)
0.9
h
R’ o
1434
N kg/day
Parameter
Values
Unit
NOx
40
g/m3
Px
654
kg/day
Xo
300
kg/day
Px + Xo
954
kg/day
QW
119
m3/day
QW/(J’netAm)
0.02
m3/m3
22Table 2.8: Biological Parameters
23Table 2.9: Sludge yield
Page | 41
24Table 2.10: Membrane calculations
Parameter
Values
Unit
Am
9887
m2
Area per element
250
m2
Actual membrane area
10000
m2
Number of elements
40
K’
120
N LMH/bar
Jnet
21
LMH
Jnet,actual
20
LMH
J’net,actual
25
N LMH
J’b
42
N LMH
J’actual
30
N LMH
Parameter
Values
Unit
Aeration Time
0.5
h/h
QA,m
4600
m3/h
Q’A,m
4729
Nm3/h
SADm
0.47
Nm3/(hm2)
SADp
19.2
Nm3/m3
MA,m
139110
kg/day
vc
225
kg
Mc
0.0065
kg/m3
25Table 2.11: Membrane Operation
26Table 2.12: Aeration Design
Parameter
Values
Unit
Tank depth
3
m
Pa,2
131
kPa
OTE membrane
0.06
%
Page | 42
OTE biological
0.14
%
Q’A,m
1.61
Nm3/s
O2 transferred by membrane aeration
24.87
kg/day
O2 required to maintain biology
1409
kg/day
Q’A,b
1.38
Nm3/s
27Table 2.13: Power Requirement
Air
blower Value
Unit
parameter
Liquid
pump Value
Unit
parameter
ξblower
0.50
Power(biological)
80.70
kW
Power(permeate) 3.44
kW
Wb
0.40
kWh/m3
Wh
0.02
kWh/m3
Power(membrane) 94.27
kW
Power(recycle)
9.11
kW
Wb,v
kWh/m3
Wp
0.04
kWh/m3
0.46
ξpump
0.45
A degree of caution is required in interpreting these data in that: a) The calculation does not account for the impact either of membrane life, which may possibly relate to permeability (which is generally higher for the FS modules), or sludge dry solids concentration on sludge disposal costs. b) There is considerable scatter in the data from which the Jnet:SADm correlations were obtained. Over the range of SADm values applied in practice for the same SADm value the operating cost of the HF module is _19% lower than that of the FS module. c) Many of the FS MBRs listed are operated without supplementary fine bubble aeration, such that the membrane aeration also provides air for bio treatment. This means that threes membranes may be over-aerated, which could also explain the higher permeabilities recorded compared with those of the HF MBRs. The one FS MBR operated with segregated membrane aeration yielded the lowest SADm value, the second lowest being that recorded for the doubledeck FS MBR
Page | 43
28Figure 2.1: Specific cost vs. flux for HS and FS technologies, flux to be related to aeration demand
29Figure 2.3: Specific cost vs. aeration demand over the ranges of aeration demand observed in practice for HF and FS technologies
Page | 44
2.3
Determination of Calculated Parameters
Pressure Calculations The net operating pressure (Pnet) for the RO systems was calculated according to the following equation: Pnet = [Pi - Po]/2 - Pp – Δπ = 0.25 bar
(1)
Where, Pnet = net operating pressure (Pa) Pi = pressure at the inlet of the pressure vessel (Pa) Po = pressure at the outlet of the pressure vessel (Pa) Pp = permeate pressure Δπ= net osmotic pressure of the feed and permeate (Pa)
The integrated averaging factor (IAF) assuming 100 percent salt rejection can be used to estimate the osmotic pressure as follows: Δπ = IAF x πf Where, πf = osmotic pressure of the feed stream (psi) IAF = 1.386 (for 50 percent recovery) Flow Calculations The net permeate rate for the MBR can be calculated using the equation:
QNET = (tON - tOFF / tON) x Qp = 23384
(2)
Where, QNET = net permeate rate (L/min) tON = the time the MBR membrane is in production (min) tOFF = the time the MBR membrane is in relaxation (min) Qp = Permeate flow rate (L/min) Please note: this calculation assumes the loss of flow during cleaning in place and intermittent maintenance cleans is negligible.
Page | 45
Flux Calculation The flux of the MBR membranes can be calculated as follows: J = (Qp x 1440) / A = 25
(3)
Where, J = Membrane flux (L/day/m2) A = Total membrane surface area (m2) Temperature Correction Low-pressure membrane fluxes are normally temperature corrected to 20ºC, and RO membranes are corrected to 25ºC. The membrane fluxes for the MBR membranes can be temperature corrected with the following formula: J @ 20 ºC = J x e-0.0239(T-20) = 122
(4)
Where, T = feed water temperature (ºC) Specific Flux The specific flux is the relationship between flux and the net operating pressure. The relationship is defined by the formula: JSP = J/PNET = 21
(5)
Where, JSP = specific flux (LMD/Pa) Salt Rejection The salt rejection for the membranes was calculated using the following equation: R = 100 x (1 – Cp/ Cf) = 1395
(6)
Where, R = rejection (%) Cp = permeate conductivity (µΩ) Cf = feed conductivity (µΩ) Hydraulic Retention Time The hydraulic retention time (HRT) was calculated using the formula: HRT = V / (QNET x 60) = 14.5
(7)
Where, HRT = Hydraulic retention time (hours) V = MBR volume (L)
Page | 46
Sludge Retention Time The sludge retention time (SRT) is defined as the total mass of activated sludge in the MBR divided by the mass flow rate of activated sludge being removed. In order to calculate the SRT of the MBRs, the reactors are treated as an ideal continuously stirred tank reactor (CSTR). Under this assumption, concentration of activated sludge in the MBR will be the same as the concentration in the waste stream and the equation will simplify as follows:
SRT = (VXR) / (QW XW) = V / QW = 25
(8)
Assuming that XR is equal to XW: Where, SRT = sludge retention time (days) XR = volatile suspended solids in the reactor (mg/L) XW = volatile suspended solids in the waste stream (mg/L) QW = waste stream flow rate (m3/day) Recycle Ratio The recycle ratio (RR) for MBR systems operating with anoxic and aerobic tanks is defined as the ratio of the flow of MLSS from the aerobic tank to the anoxic tank, divided by the net permeate rate. The RR of MBR is calculated as follows: RR = (QR-membrane - QNET) / QNET = (QR / QNET) – 1
(9)
Where, RR = Recycle Ratio 2.4
Sizing of the MBR
Packing density given by ratio of fibre surface area to volume Φ = Af / V
(1)
Where Af = surface area of fibres
= Nπdf
(2)
= Nπdf 2/4
(3)
V = module volume Av = volume occupied by fibres So: Av/ Af = df / 4
(4)
Thus: Ax = (4V – df Af) / 4L
(5)
Page | 47
Where Ax = free x-sectional area
So: QA = 3600U / 4L x (4V - – df Af)
(6)
Where QA = aeration rate in m3/hr U = air flow velocity in channels (m/s) SADm = 3600U / 4V x (4V/Af – df)
(7)
Where SADm = aeration demand with respect to fibre area Substituting for V/Af and normalizing against flux: SADp = 3.6x106U / 4LJ x (4/ Φ – df)
(8)
Where SADp = aeration demand with respect to permeate volume Evidence suggests that J is a linear function of aeration intensity: J = mU + c
(9)
Where m and c are empirical constants So: SADp = 3.6x106U / 4L (mU + c) x (4/ Φ – df)
(10)
Aeration energy demand in kWh/m3 permeate is then given by EA = 0.0303 SADp γ x [((10x + 101) / 101)(1 – 1/ γ) – 1] / (γ – 1) ζ (11) Where γ = aerator constant = 1.4 ζ = blower efficiency = 0.5 x = aerator depth = 3 m So: EA = Uk / L (mU + c) x (4/ Φ – df)
(12)
Where K = 0.0303 x 3.6x106 / 4 x γ x [((10x + 101) / 101) (1 – 1/
γ)
– 1] / (γ – 1) ζ and is thus
constant for a given system. Now, commercial technical data for available membrane modules (Judd, 2006) suggests that, for packing density and fiber diameter respectively in m-1 and m: 1 / Φ ≈ gdf + 0.001 f
(13)
Where f = 0.7-1.7 and g = 0.9-1.1 Thus
Page | 48
EA = Uk / L (mU + c) x [(4/g-1) df + 0.004f)
(14)
For the four main MBR HF membrane suppliers, g = 0.89 (R2 = 0.97) and f = 1.7, and thus:
EA = Uk / L (mU + c) x [3.5 df + 0.0068]
2.5
(15)
Summary
The selection of appropriate design and operating parameter values for an iMBR centers on: choice of membrane module; choice of membrane aerator, if the membrane module is not provided with an integral aerator; Membrane aeration rate. Many, if not all, of these facets are stipulated by the technology provider, and the choice of technology itself (including that between iMBR and sMBR) will be strongly influenced by the duty to which it is being put. However, broadly speaking the mean permeability sustained in an iMBR is dependent on the aeration rate. Failure of membrane surface fouling, which can be irrecoverable, and clogging of the membrane channels. It is therefore essential that the maintenance schedule includes cleaning of the aerators, normally achieved by flushing with a water or hypochlorite solution. Design of iMBRs relies on accurate information regarding oxygen transfer to the biomass and maintenance of permeability by membrane aeration. The design proceeds via calculation of the oxygen demand of the biomass, which relates primarily to the feed water composition, the solids retention time and the oxygen transfer efficiency. This procedure applies to all bio treatment processes. However, for an MBR complications arise when estimating the oxygen transfer and hydraulic performance (flux and permeability) provided by the membrane aeration. The correlation of membrane flux and permeability with membrane aeration rate and the applied cleaning protocol relies entirely on heuristically-derived information. Minor: Oil-Water Separator
Page | 49
2.6
Oil-Water separator design
Oil-water separation theory is based on the rise rate of the oil globules (vertical velocity) and its relationship to the surface-loading rate of the separator. The rise rate is the velocity at which oil particles move toward the separator surface as a result of the differential density of the oil and the aqueous phase of the wastewater. The surface-loading rate is ratio of the flow rate to the separator to the surface area of the separator. The required surface-loading rate for removal of a specified size of oil droplet can be determined from the equation for rise rate. The following parameters are required for the design of an oil-water separator: a) Design flow (Qm), the maximum wastewater flow. The design flow should include allowance for plant expansion and storm water runoff, if applicable. b) Wastewater temperature. Lower temperatures are used for conservative design. c) Wastewater specific gravity (Sw). d) Wastewater absolute (dynamic) viscosity (µ). Note: Kinematic viscosity (v) of a fluid of density (ρ) is v = µ /ρ. e) Wastewater oil-fraction specific gravity (So). Higher values are used for conservative design. f) Globule size to be removed. The nominal size is 0.015 centimeters (150 micrometers), although other values can be used if indicated by specific data.
The design of conventional separators is subject to the following constraints: a) Horizontal velocity (vH) through the separator should be less than or equal to 1.5 cm/s (0.015 m/s) or equal to 15 times the rise rate of the oil globules (Vt), whichever is smaller. b) Separator water depth (d) should not be less than 1 m, to minimise turbulence caused by oil/sludge flight scrapers and high flows. Additional depth may be necessary for installations equipped with flight scrapers. It is usually not common practice to exceed a water depth of 2.4 m. c) The ratio of separator depth to separator width (d/B) typically ranges from 0.3 to 0.5 in refinery services.
Page | 50
d) Separator width (B) is typically between 1.8 and 6 m in refinery services. e) By providing two separator channels, one channel is available for use when it becomes necessary to remove the other from service for repair or cleaning. f) The amount of freeboard specified should be based on consideration of the type of cover to be installed and the maximum hydraulic surge used for design. g) A length-to-width ratio (L/B) of at least 5 is suggested to provide more uniform flow distribution and to minimize the effects of inlet and outlet turbulence on the main separator channel.
30Figure 2.4: Design variables for oil interceptors.
The oil-globule rise rate (Vt) can be calculated by Equation 1 or 2 shown below. Equation (1) should be used when the target diameter of the oil globules to be
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removed is known to be other than 0.015 cm and represents a typical design approach. Equation (2) assumes an oil globule size of 0.015 cm. Vt = g/18µ(ρw – ρo)D2 Vt = 0.0123[(Sw – So)/µ, (Where D = 0.015cm) Where: Vt = vertical velocity, or rise rate, of the designed oil globule, in cm/s. g = acceleration due to gravity (981 cm/s2) µ = absolute viscosity of wastewater at the design temperature, in poise ρw = density of water at the design temperature, in g/cm3 ρo = density of oil at the design temperature, in g/cm3 D = diameter of oil globule to be removed, in cm Sw = specific gravity of the wastewater at the design temperature (dimensionless) So = specific gravity of the oil present in the wastewater (dimensionless) Alternatively, if using kinematic viscosity equations 1 and 2 may be rearraged as follows: Vt = g/18v(1-So)D2 Vt = 0.0123(1-So/v) Where, V = kinematic viscosity of the wastewater at the design tempearature,in stokes. Horizontal Velocity (vH) The design mean horizontal velocity is defined by the smaller of the values for vH in cm/s obtained from the following two constraints:
Minimum Vertical Cross-Sectional Area (Ac) Using the design flow to the separator (Qm) and the selected value for horizontal velocity (vH), the minimum total cross-sectional area of the separator (Ac) can be determined from the following equation: Ac = Qm x 100/ VH Where: Ac = minimum vertical Cross- sectional area, in m2 Qm = design flow to the separator, in m3/s VH = horizontal velocity, in cm/s
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Channel Width and Depth Given the total cross-sectional area of the channels (Ac) and the number of channels desired (n), the width and depth of each channel can be determined. A channel width (B), generally between 1.8 - 6 m, should be substituted into the following equation, solving for depth (d): d = Ac/Bn Where: d = depth of channel, in m B = width of channel, in m Separator Length Once the separator depth and width have been determined, the final dimension, the channel length (L), is found using the following equation: L = F(VH/Vt)d Where: L = length of channel, in m F = turbulence and short-circulated factor (dimensionless) VH = horizontal velocity, in cm/s D = depth of channel, in m If necessary, the separator’s length should be adjusted to be at least five times its width, to minimize the disturbing effects of the inlet and outlet zones. Equation is derived from several basic separator relations: a) The equation for horizontal velocity (vH = Qm/Ac/), where Ac is the minimum total cross-sectional area of the separator. b) The equation for surface-loading rate (Vt = Qm/AH), where AH is the minimum total surface area of the separator. c) Two geometrical relations for separator surface and cross-section area (AH = LBn and Ac= dBn), where n is the number of separator channels. The turbulence and short-circuiting factor (F) is a composite of an experimentally determined short-cutting factor of 1.21 and a turbulence factor whose value depends on the ratio of mean horizontal velocity (vH) to the rise rate of the oil globules (Vt). A
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graph of F versus the ratio vH/Vt is given in Figure1.5; the data used to generate the graph are also given below. 31Figure 2.5: Recommended values of F for various values of Vh/Vt
Minimum Horizontal Area In an ideal separator - one in which there is no short-circuiting, turbulence, or eddies – the removal of a given suspension is a function of the overflow rate, that is, the flow rate divided by the surface area. The overflow rate has the dimensions of velocity. In an ideal separator, any oil globule whose rise rate is greater than or equal to the overflow rate will be removed. This means that any particle whose rise rate is greater than or equal to the water depth divided by the retention time will reach the surface, even if it starts from the bottom of the chamber. When the rise rate is equal to the overflow rate, this relationship is expressed as follows:
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Vt = di/Ti = 100di/(LiBidi/Qm) = 100Qm/LiBi = Vo Where: di = depth of wastewater in an ideal separator, in cm Ti = retention time in an separator, in s Li = length of an ideal separator, in cm Bi = width of an ideal separator, in cm Qm = design flow to the separator, in m3/s Vo = overflow rate, in cm/s
The equation establishes that the surface area required for an ideal separator is equal to the flow of wastewater divided by the rise rate of the oil globules, regardless of any given or assigned depth. By taking into account the design factor (F), the minimum horizontal area (AH), is obtained as follows: AH = F(Qm x 100/Vt) Where: AH = minimum horizontal area, in m2 F = turbulence and short-circuit factor Qm = design flow to the separator, in m3/s Vt = vertical velocity, or rise rate, of the designed oil globule, in cm/s. Qm/AH = 0.00196(Sw – So)/µ Maintenance Parallel-plate units may experience clogging problems if the plate inclination is too shallow or the plate-to-plate spacing is too narrow. It has also been reported that sand entering the plate system can collect at the entrance to the plate assembly and reduce flow through the lower plate sections. Should blockages develop, they may be cleared by removing the accumulated solids, flushing the plate pack with water or air, or mechanical cleaning. Operating and maintenance manuals and equipment suppliers should be consulted with regard to approved procedures. Solids accumulation and clogging should be considered before installation and designed for accordingly.
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Parallel-plate packs do not generally clog if they are properly designed, installed, and maintained. If significant solids levels are expected, the plate inclination should be about 60o, which exceeds the angle of repose of practically all solids encountered in such systems. A plate slope of 60o and periodic blowdown of accumulated solids should help to avoid most parallel-plate separator plugging problems. Construction Details A variety of parallel-plate equipment configurations are commercially available. In the case of conventional separators retrofitted with parallel plates few, if any, additional fitments are required in addition to those already present. New parallelplate separators have a wide range of design features and may be purchased as packaged units, with oil and sludge-draw off equipment provided. Consequently, specific construction and fitment details are omitted from this subsection. Two major types of parallel-plate separators are marketed: the cross-flow inclined plate and the down-flow inclined plate. Cross-flow separators that employ parallel plates oriented vertically and horizontally are also available, although there are few applications for them in wastewater treatments. In a cross-flow separator, shown in sketch bellow, flow enters the plate section from the side and flows horizontally between the plates. Oil and sludge accumulate on the plate surfaces above and below the wastewater flowing between the plates. As the oil and sludge build up, the oil globules rise to the separator surface and sludge gravitates toward the separator bottom. In a down-flow separator, the wastewater flows down between the parallel plates, sludge deposited on the lower plates flows to the bottom of the separator, and oil accumulated beneath the upper plate flows counter-current to the waste flow to the top of the separator.
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32Figure 2.6: sketch of Parallel plate separator - cross-flow
[Courtesy of Sepa Waste Water Treatment Pty. Ltd., Australia] Terminal Velocity of Oil Globules in Water The basic principles of separation by gravity differential can be expressed mathematically and applied quantitatively. When a particle is allowed to move freely in a fluid and is subjected to gravitational force, its rising or settling velocity with respect to the fluid becomes a constant when the resistance to motion equals the weight of the particle in the fluid. In other words, the resistance to motion of a particle in a liquid medium is equal to the effective weight of the particle when the terminal velocity has been reached, namely, when the acceleration caused by gravity becomes zero. The general equation for this resistance, first proposed by Newton, is as follows: Df = CA(ρwV2/2) Where: Df = Particle’s resistance to motion in liquid medium, in dynes C = Coefficient of drag A = projected area of oil globules, in cm2 ρw = density of water, in g/cm3 V = terminal velocity of oil globule in water, in cm/s The equation for the effective weight of the particle is as follows:
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W = ( D3/6) x ( ρw – ρo)g Where: W = effective weight of the oil globule in water, in dynes D = diameter of oil globule, in cm ρo = density of the oil globule, in g/cm3 g = acceleration caused by the force of gravity (981 cm/s2) Equating equations above: CA(ρwV2/2) = (πD3/6) x ( ρw – ρo)g Given that, for a sphere, A = D2/4 Then the rate of rise is as follows:
The equation for the resistance to motion of a small spherical particle at its terminal velocity is as follows:
Where: µ = absolute viscosity of wastewater the design temperature, in poises If W in Equation above is equated to Df in Equation 16, a new expression for V is obtained. By the substitution of Vt, the oil globules’ velocity of rise (in cm/s) for the general term V, the well-known form of Stokes’ law for the terminal velocity of spheres in a liquid medium becomes applicable to the rate of rise of oil globules in water. Equations should theoretically include a deformation coefficient that depends on the relative viscosities of the oil and the water; however, in practice, the coefficient is not required to estimate the rate of rise of small oil globules in wastewater.
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Where: Cv = deformation coefficient theoretically applicable µ1 = absolute viscosity of the particle, in poises µ2 = absolute viscosity of the medium, in poises If this correction for internal flow is applied to Equation 17, Stokes’ law for determining the rate of rise of an oil particle in water would become the following:
Equations above are strictly correct only when the rising particle’s Reynolds number (based on the particle diameter) is less than 0.5. For the range of Reynolds numbers resulting from the computations in this chapter (all substantially less than unity), however, the deviation from Stokes’ law is negligible for design purposes. Size and Gravity of Oil Globules From the results of experiments and from plant operating data, it has been determined that the design of wastewater separators should be based on the rise rate of oil globules with a diameter of 0.015 cm (150 micrometers). To check the dimensions of this formula, it is necessary to note that the number 0.0123 was obtained from dimensional factors and therefore has the dimensions of its factors, which are as follows:
If the globule diameter is 60 micrometers (i.e., D = 0.006), the factor is 0.0020, rather than 0.0123. Derivation of Equation for Separator Length Separator length is calculated from the following equation: L = F(vH/vt)d
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The basis equations used to derive the equation for separator length are AH = FQm/vt ; Ac = Qm/ vH; Ac = dBn Therefore; L = AH/Bn = AH/(Ac/d) = AHd/Ac = [(FQm/ vt) x d] / (Qm/ vH) L = L = F(vH / vt)d Where: AH = total separator surface area L = length of separator channel B = widthof separator channel N = number of separator channels F = turbulence and short-circuiting factor Qm = total design flow to separator Ac = separator’s total cross sectional area vH = separator’s horizontal velocity vt = separators surface-loading rate d = depth of separator channel Calculation and results Data Given:
Sewage Flow = 70000 m3/day = 0.8102 m3/s
Temperature = 29 °C
Assumptions taken:
Specific gravity of water = 0.99
Specific gravity of oil = 0.92
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Viscosity of wastewater = 0.0062 poise = 0.3871 cm2/s
Oil globule size = 0.015 cm
Design constraints •
VH ≤ 1.5 cm/s or VH = 15 Vt, whichever the smaller
•
1.0 m ≤ d ≤ 2.5 m
•
0.3 ≤ d/B ≤ 0.5
•
1.8 m ≤ B ≤ 6.0 m
•
n = 2 (minimum 2 channels)
•
L/B ≥ 5
Calculating Vt using: Vt = 0.0123[(Sw - So)/μ] Vt = 0.0123[(990 – 920)/ (0.3871)] Vt = 2.224 cm/s Vertical Velocity = 2.224 cm/s Horizontal flow velocity is taken as 1.5 cm/s Ac = (0.8102 x 100)/1.5 Ac = 54 m2 Therefore the minimum vertical cross-sectional area is 54 m2 Similarly, By assuming ‘B’ to be 8m and n = 2 d = 54/ (8 x 2) d =3.38 m Depth of channel = 3.38 m
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Depth/width ratio = 3.38/8 = 0.4 Calculating L using: Using the following graph:
F is found to be 1.46 Hence, L = F x (VH/Vt) x d L = 1.46 x (1.5/2.224) x 3.38 L = 1.46 x 0.67446 x 3.38 L = 3.33 m Length of channel = 3.33 m
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Design inputs: Sewage Flow (in m3/s)
0.8102
Temperature (in °C)
29
Specific gravity of water
0.99
Specific gravity of oil
0.92
Viscosity of wastewater (in poise)
0.0062
Oil globule size (in cm)
0.015
Results: Vertical Velocity (in cm/s)
0.18083
Horizontal flow velocity ( in cm/s)
1.5
minimum vertical cross-sectional area (in m2)
54
number of channels
2
Width of channel (in m)
8
Depth of channel (in m)
3.38
Length of channel (in m)
3.33
2.7
PIPE SELECTION AND PIPE SIZING FOR MBR TANKS OUTLETS AND INLETS
Pipe Selection When it comes to pipes for transportation of liquids, we are exposed to a variety of the pipes which normally are made of plastic, concrete or metal (e.g. galvanized iron or copper and stainless stain) to make our choices. However, if we consider the cost of copper for the transportation of effluent of a treatment plant, it is definitely not feasible. Similarly while opting for a particular pipe material for transportation of liquids the key factors that need to be considered are: water characteristics and chemistry and resistant against a specified internal and external pressure. Thus to start with the primary factor is the water chemistry and characteristics which include pH, salts that are dissolved in the water and among other. Likewise it is be noted that there would be an alteration in the initial pH of the effluent since the latter has been
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subjected to a coagulation and flocculation process with help of alum which has the tendency to render the effluent to be slightly more acidic: pH changes from 6.5 to approximately 4.7 (Tchobanoglous, et al., 2004). Subsequently we can expect the corrosiveness of the effluent to material to increase; thus the prime requirement for the pipe material would be higher corrosion resistance. Hereby the choice of metal as pipe material can be crossed from the initial list; therefore the best suited pipe material for the MBR is plastic. The raw material needed to make most plastic comes from petroleum and natural gas. Due to their relatively low costs, ease in manufacture, versatility and imperviousness to water, plastics are used in an enormous and expanding range of products: from paper clips to pipes intended for transporting drinking water. Plastic has replaced many common materials such as cement and metals within drinking water networks (WECF, 2012). Plastics are often preferred than metals due to a number of intrinsic advantages: plastic piping is lightweight and does not require an open flame for joining the flexibility of plastic can simplify the installation. Plastics are typically lower in cost and resist the corrosion and scaling that plague metals in some applications. However, indication of the mitigation of synthetic chemical contaminants from plastic pipe materials to water may exist. These contaminants likely occur at low “safe levels”, but are sufficient to generate odor and taste concerns in some cases. Another disadvantage of some types of plastic pipes is that they have lowered resistance to chlorinated water; which will be not problematic in our case. Likewise the most common types of plastic used in water and wastewater applications are PE (Polyethylene) pipes and PVC (Polyvinyl chloride) pipes (WECF, 2012)... PE (Polyethylene) pipes There are basically three of PE (Polyethylene) pipes: high-density polyethylene (HDPE), medium density (MDPE) and low density (LDPE) pipes. The level of density expresses the pressure that the pipes can sustain. For locations enduring high pressure or weight, like streets, HPPE pipes are used. Performances of PE pipes of different manufactures show different possible temperature ranges in terms of application and usually range between -20 and + 900C. PE pipes are widely used for water and
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sanitation systems. High-quality PE pipes have a long lifetime (50 years) and are easy to maintain. They have high impact strength and show resistance to cracking even at low temperatures. PE pipes are also stable in water and do not tend to corrode (WECF, 2012). PVC (Polyvinyl chloride) pipes PVC is the third most widely produced plastic after PE and PP (polypropylene). PVC is widely used in construction because it is cheap, durable and easily workable but nevertheless the material tends to get brittle in the long- term. Simultaneously from an environmental point of view the usage of PVC is controversial, particularly because of the harmful chemicals (e.g. dioxins) which may be released in the environment during its production and final disposal (burning) (WECF, 2012).. Finally it can be concluded that a medium density polyethylene (MDPE) pipe is best suitable for the Membrane biological reactor tank: due to the versatility of being corrosion resistance and also sustain pressure to which it would be exposed to. In addition its low cost relative to other pipe material like copper and extended lifetime render it to be more attractive. Pipe sizing There are basically two methods reported by Sinnott, 2005 through which we can proceed to evaluate the optimum diameter of a pipe: either using economic pipe diameter formula or Simpson correlation (1968). However due to lack of information related to economic pipe diameter for medium density polyethylene we will go by Simpson correlation. Simpson (1968) gives values for the optimum velocity in terms of the fluid density. His values, converted to SI units and rounded, are:
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33Table 2.14: Fluid density and Velocity
Similarly together with the Simpson correlation we shall abide by the following assumptions for the evaluating of the optimum diameter. a) The piping system should be designed for the maximum flow-rate output from the MBR tank that is 50000 m3/hr. However to increase the reliability and not to oversize the pump and piping system; we will assume that delivery of 3125 m3 of effluent will be performed by three pumps and we have one additional stand by pump for any contingency. b) Usually we can expect the temperature of the effluent to experience a drop. likewise the temperature drop will somehow be dependent on the season prevailing in the country, however since we lack data to evaluate any raise or drop we will simply assume that the temperature of the effluent remain at 25℃. c) The density of the effluent is similar to that water at 250C: 997.048kg/m3; the ideology behind this assumption is that the effluent before entering the MBR is subjected to several pre-treatment namely: oil and grease removal, grit removal and coagulation and flocculation process which will enable the removal of several contaminants which otherwise might influence its density at 250C. d) The viscosity of effluent is again similar to that of water at 25 0C: 0.890 x 10-3 Ns/m2 and the same ideology as density applies for viscosity. Calculations If we consult the fluid density and optimum velocity table by Simpson is can be noted that we do not have any specific optimum velocity value for a fluid density of
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997.048kg/m3; thus by graphical interpolation of the data was performed to estimate the optimum velocity of the fluid and found to be 2.7 m/s.
Consequently the internal diameter of the pipes for MBR is evaluated to be 40 cm. 2.8
Pump selection for MBR
Pumps are generally classified in two classes: 1. Dynamic pumps, such as centrifugal pumps. 2. Positive displacement pumps, such as reciprocating and diaphragm pumps. Pump selection is made on the flow rate and head required, together with other process considerations, such as corrosion or the presence of solids in the fluid. Table 2.15 provides a brief description and application of many types of pumps in these two classes. 34Table 2.15: Pump Types and Major Applications in Wastewater treatment
Major Classification
Pump Type
Major Pumping Application Raw water and wastewater,
Centrifugal
secondary sludge return and wasting, settled primary and thickened sludge, effluent
Kinetic Peripheral Rotary
Scum. grit, sludge and raw water and wastewater Lubricating oils, gas engines,
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chemical solutions, small flows of water and wastewater Scum and primary, secondary, Plunger
and settled sludge; chemical solution Secondary
Airlift
sludge
circulation
and wasting, grit
Positive Displacement Pneumatic ejector
Raw wastewater at small installation (100 to 600 L/min) Grit, settled primary and
Screw
secondary sludge, thickened sludge, raw wastewater
Diaphragm
Chemical solution
Source: (Spellman, 2003) Considering the data obtained from table above it can be said that the best suited pump for pumping effluent from the MBR is the centrifugal pump. In addition the centrifugal pump is by far the most widely used type in the chemical and petroleum industries. Furthermore with its ability to pump liquids with very wide-ranging properties and suspensions with a high solid content including, for example, cement slurries, and clearly demonstrate the superiority among of the latter other pumps in wastewater applications. Likewise it may be constructed from a very wide range of corrosion resistant materials. The whole pump casing may be constructed from plastics such as polypropylene or it may be fitted with a corrosion resistant lining. Because it operates at high speed, it may be directly coupled to an electric motor and it will also give a high flow-rate for its size (Sinnott, 2005). 2.9
Power requirements for pumps in MBR
To transport a liquid from one vessel to another through a pipeline energy has to be supplied to: 1. Overcome the friction losses in the pipes;
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2. Overcome the miscellaneous losses in the pipe fittings (e.g. bends), values, instruments, etc. 3. Overcome the losses in process equipment (e.g. primary clarifier); 4. Overcome any difference in elevation from end to end of the pipe; 5. Overcome any difference in pressure between the vessels at each of the pipeline. Hence the total energy required can be calculated from the equation: g∆z + ∆P/ρ - ∆Pf/ρ – W = 0 Where: W = work done, J/kg ∆z = difference in elevation (z1 – z2), m ∆P = difference in system pressure (P1 – P2), N/m2 ∆Pf = pressure drop due to friction, including miscellaneous losses, N/m2 ρ = Liquid density, kg/m3 g =acceleration due to gravity, m/s2 Similarly the head required from the pump = ∆P/ρg - ∆Pf/ρg - ∆z Total head required will be the sum of the dynamic head due to friction losses in the piping, fittings, valves and process equipment, and any static head due to differences in elevation. Pressure drop in pipelines The pressure drop in a pipe, due to friction, is a function of the fluid flow-rate, fluid density and viscosity, pipe diameter, pipe surface roughness and the length of the pipe. It can be calculated using the following equation: ∆Pf = 8f(L/di)ρu2/2 Where: ∆Pf = pressure drop, N/m2
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F = friction factor L = pipe length, m di = pipe inside diameter, m ρ = fluid density, kg/m3 u = fluid velocity, m/s The friction factor is a dependent on the Reynolds number and pipe roughness. The friction factor for use in equation 2.8.1 can be found from Figure 2.7
Where:
Relative roughness, e = absolute roughness/pipe inside diameter Note: the friction factor used in equation 5.3 is related to the shear stress at the pipe wall, R, by the equation:
Miscellaneous pressure losses In addition to pressure loss in pipelines, any obstruction to flow will generate turbulence and cause a pressure drop. So, pipe fittings, such as: bends, elbows, reducing or enlargement sections, and tee junctions, will increase the pressure drop in a pipeline. There will also be a pressure drop due to the valves used to isolate equipment and control the fluid flow. The pressure drop due to these miscellaneous losses can be estimated using either of two methods: 1. As the number of velocity heads, K, lost at each fitting or valve. A velocity head is u2/2g, meters of the fluid, equivalent to (u2/2) ρ, N/m2. The total number of
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velocity heads lost due to all the fittings and valves is added to the pressure drop due to pipe friction (Sinnott, 2005). 2. As a length of pipe that would cause the same pressure loss as the fitting or valve. As this will be a function of the pipe diameter, it is expressed as the number of equivalent pipe diameters. The length of pipe to add to the actual pipe length is found by multiplying the total number of equivalent pipe diameters by the diameter of the pipe being used (Sinnott, 2005). The number of velocity heads lost, or equivalent pipe diameter, is a characteristic of the particular fitting or type of valve used. Values can be found in handbooks and manufacturers’ literature. Summary of results With help of the literature review above the calculations were performed and the main results have been tabulated below. 35Table 2.17: Summary of result involving the main pipeline connecting the MBR
Pipeline description
Pipeline between primary Output pipeline of MBR clarifier to MBR tank
Pipeline length Optimum
flow-rate
26 m of 5000 m3/hr
33 m 5000 m3/hr
effluent Optimum Pipe Diameter
40 cm
40 cm
Reynolds number
1.03×106
1.3×106
Friction factor
0.0065
0.0065
Miscellaneous losses in
284 m
86 m
Pressure drop in pipeline
95.52 kPa
108.12 kPa
Effective pressure drop in
280.52 kPa
108.12 kPa
Power requirement
149.04 J/kg
137.81 J/kg
Head required
15.19 m
3.63 m
equivalent pipe diameter
pipeline
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CHAPTER 3: Heat and material Balance 3.1
Material Balance for the MBR
I.
Mass Balance on the MBR
Influent = Waste Sludge + Effluent
Q = Influent Flowrate
SE = BOD in Effluent, 𝑚𝑔⁄𝐿
S0 = BOD in influent, 𝑚𝑔⁄𝐿
Hence BOD efficiency can be calculated as follows: Given: BOD in domestic wastewater entering Primary Settling Tank = 307 𝑚𝑔⁄𝐿 Assuming BOD removal efficiency in primary clarifier = 40 % Primary effluent BOD = 307 𝑚𝑔⁄𝐿 × (1 − 0.40) = 184 𝑚𝑔⁄𝐿 Therefore; As assumed permissible limits, that is 40 mg/L = 2800 kg/day is in the effluent BOD Removal Efficiency in MBR =
184 𝑚𝑔⁄𝐿 −40𝑚𝑔⁄𝐿 184𝑚𝑔⁄𝐿
× 100 = 78%
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307 𝑚𝑔⁄𝐿 −40𝑚𝑔⁄𝐿 )× 307𝑚𝑔⁄𝐿
Hence; 𝑂𝑣𝑒𝑟𝑎𝑙𝑙 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 = (
100 = 87%
The recycle ratio can be expressed as follows: 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝐹𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑚3 ⁄𝑑𝑎𝑦 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝑅𝑎𝑡𝑖𝑜 = 𝐼𝑛𝑓𝑙𝑢𝑒𝑛𝑡 𝐹𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑚3 ⁄𝑑𝑎𝑦 Typical recycle ratio for conventional activated sludge process = 0.25 – 0.50 Average Recycle Ratio = 0.375 Therefore; 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝐹𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑄𝑅 = 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝑟𝑎𝑡𝑖𝑜 × 𝐼𝑛𝑓𝑙𝑢𝑒𝑛𝑡 𝑓𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑄0 = 0.375 × 70000 𝑚3 ⁄𝑑𝑎𝑦 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝐹𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑄𝑅 = 26250 𝑚3 ⁄𝑑𝑎𝑦 Also by the methodology of Shu Dar lin (2005), 𝑄𝑅 can be expresses as follows: 𝑄𝑅 =
𝑄0 (𝑥 − 𝑥0 ) 𝑥𝑤 − 𝑥
Whereby: X = MLSS concentration, 2500 𝑚𝑔⁄𝐿 X0 = Primary Effluent TSS, 102.6 𝑚𝑔⁄𝐿 𝑄𝑅 = 𝑟𝑒𝑐𝑦𝑐𝑙𝑒 𝑓𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 26250 𝑚3 ⁄𝑑𝑎𝑦 26250 𝑚3 ⁄𝑑𝑎𝑦 =
70000 𝑚3 ⁄𝑑𝑎𝑦 (2500 𝑔⁄𝑚3 − 102.6 𝑔⁄𝑚3 ) 𝑥𝑤 − 2500 𝑔⁄𝑚3 𝑥𝑤 = 3893.07 𝑔⁄𝑚3
Also; 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝑅𝑎𝑡𝑖𝑜 =
𝑄𝑅 𝑋 = 𝑄0 𝑋𝑅 − 𝑋
Whereby: 𝑋𝑅 is the concentration in recycle sludge and as assumed R is 0.375.
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2500 𝑔⁄𝑚3 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝑅𝑎𝑡𝑖𝑜 = 𝑋𝑅 − 2500 𝑔⁄𝑚3
Inlet Flowrate:XO = Concentration of TSS in influent Primary Settling Tank Outlet Flowrate:Xe = Concentration of Biomass in effluent Return Sludge: QR = return flow pumping rate, 𝑚3 ⁄𝑑𝑎𝑦 Xu = return microorganism concentration Waste Activated Sludge: QW = Waste flow from recycle waste line, 𝑚3 ⁄𝑑𝑎𝑦 And µ = growth of solids (𝑑𝑎𝑦 −1 )
II.
BOD Balance around MBR
𝐼𝑛𝑝𝑢𝑡 − 𝑜𝑢𝑡𝑝𝑢𝑡 + 𝑔𝑒𝑛𝑒𝑟𝑎𝑡𝑖𝑜𝑛 = 𝑎𝑐𝑐𝑢𝑚𝑢𝑙𝑎𝑡𝑖𝑜𝑛 (𝑄0 𝑆0 + 𝑄𝑅 𝑆𝐸 ) − (𝑄0 + 𝑄𝑅 )𝑆𝐸 −
𝜇𝑋𝑉 𝑑𝑆 = 𝑉 𝑌 𝑑𝑡
𝑑𝑆 𝑉=0 𝑑𝑡 Y = cell yield in kg MLSS/ kg BOD removed At steady state 𝜇𝑋𝑉 = 𝑄0 𝑆0 − 𝑄0 𝑆𝐸 𝑌 𝜇 𝑄0 (𝑆0 − 𝑆𝐸 ) = 𝑓⁄𝑚 𝑟𝑎𝑡𝑖𝑜 = 𝑌 𝑉𝑥 𝑆0 = 184 𝑚𝑔⁄𝐿 Assuming no chemical changes occur: 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝐵𝑂𝐷𝐸 = 40 𝑚𝑔⁄𝐿 Therefore:
Page | 74
𝐵𝑂𝐷𝑅 = 𝐵𝑂𝐷𝑊𝐴𝑆 = 40 𝑚𝑔⁄𝐿 III.
Flow Balance
Influent Flow Q0 = 70,000 m3/day Initial BOD = BOD0 = 184 g/m3 As calculated: BOD Efficiency = 78 % BOD in Effluent = 40 g/m3 IV.
Solid Balance on membrane
𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑇𝑆𝑆 𝑖𝑛 𝑅𝐴𝑆 = 𝑇𝑆𝑆𝑅 = 𝑋𝑈 𝑔⁄𝑚3 × 𝑄𝑅 𝑚3 ⁄𝑑𝑎𝑦 𝑇𝑆𝑆𝑅 = 10.65 𝑘𝑔⁄𝑚3 × 26250 𝑚3 ⁄𝑑𝑎𝑦 = 279,562.5 𝐾𝑔⁄𝑑𝑎𝑦 𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑇𝑆𝑆 𝑖𝑛 𝑊𝐴𝑆 = 𝑋𝑢 𝑘𝑔⁄𝑚3 × 𝑄𝑊 𝑚3 ⁄𝑑𝑎𝑦 = 2367.07 𝑘𝑔⁄𝑑𝑎𝑦 Assume TSS Removal Efficiency = 81% Therefore: 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑂𝑓 𝑇𝑆𝑆 𝑖𝑛 𝐸𝑓𝑓𝑙𝑢𝑒𝑛𝑡 = 0.19 × 102.6 𝑚𝑔⁄𝐿 = 19.494 𝑚𝑔⁄𝐿 = 1364.6 𝑘𝑔⁄𝑑𝑎𝑦 V.
Balance on VSS on membrane
The removal efficiency of VSS in an MBR system is 90%, therefore; 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑟𝑖𝑜𝑛 𝑜𝑓 𝑉𝑆𝑆 𝑖𝑛 𝐸𝑓𝑓𝑙𝑢𝑒𝑛𝑡 = 10% × 82.08 𝑔⁄𝑚3 = 8.208 𝑔⁄𝑚3 = 574.6𝑘𝑔⁄𝑑𝑎𝑦 Whereby VSS = 80% TSS = 82.08𝑔⁄𝑚3 = 5745.6𝑘𝑔⁄𝑑𝑎𝑦 Assuming: 𝑉𝑆𝑆𝑊𝐴𝑆 = 𝑉𝑆𝑆𝑅 = 5745.6 𝐾𝑔⁄𝑑𝑎𝑦 − 574.6 𝐾𝑔⁄𝑑𝑎𝑦 = 5171.04 𝑘𝑔⁄𝑑𝑟𝑦 VI.
NH3-N Balance on the membrane skid
Overall Balance:
Page | 75
𝑁𝐻3 − 𝑁𝑖𝑛 = 𝑁𝐻3 − 𝑁𝑜𝑢𝑡 𝑁𝐻3 − 𝑁𝑂𝑈𝑇 = 𝑁𝐻3 − 𝑁𝐸 + 𝑁𝐻3 − 𝑁𝑊𝐴𝑆 By the methodology of N.F.Gray, 2005, the removal efficiency of 𝑁𝐻3 − 𝑁 in an ASP system is 90% 𝑁𝐻3 − 𝑁𝑖𝑛 = 1400 𝐾𝑔⁄𝑑𝑎𝑦 𝑁𝐻3 − 𝑁 𝑟𝑒𝑚𝑜𝑣𝑒𝑑 𝑖𝑛 𝑎𝑒𝑟𝑎𝑡𝑒𝑑 𝑡𝑎𝑛𝑘 = 90% × 1400 𝐾𝑔⁄𝑑𝑎𝑦 = 1260 𝑘𝑔⁄𝑑𝑎𝑦 𝑁𝐻3 − 𝑁𝐸 = 𝑁𝐻3 − 𝑁𝑊𝐴𝑆 = 𝑁𝐻3 − 𝑁𝑅 = 1400 𝐾𝑔⁄𝑑𝑎𝑦 − 1260 𝐾𝑔⁄𝑑𝑎𝑦 = 140 𝑘𝑔⁄𝑑𝑎𝑦 VII.
NO3-N Balance on membrane skid
Overall Balance: 𝑁𝑂3 − 𝑁𝑖𝑛 = 𝑁𝑂3 − 𝑁𝑜𝑢𝑡 Since nitrification occurs, let 𝑁𝑂3 − 𝑁𝑥 be the amount of nitrates obtained by the nitrification of ammonia. Therefore: 𝑁𝑂3 − 𝑁𝑖𝑛 = 𝑁𝑂3 − 𝑁1 + 𝑁𝑂3 − 𝑁𝑥 Assuming 𝑁𝑂3 − 𝑁𝑥 = 5031.2 Kg⁄day 𝑁𝑂3 − 𝑁𝑜𝑢𝑡 = 𝑁𝑂3 − 𝑁𝐸 + 𝑁𝑂3 − 𝑁𝑊𝐴𝑆 𝑁𝑂3 − 𝑁𝑥 + 𝑁𝑂3 − 𝑁𝑖𝑛 = 𝑁𝑂3 − 𝑁𝐸 + 𝑁𝑂3 − 𝑁𝑊𝐴𝑆 According to N.F.Gray (2005), Removal Efficiency=90% Since 𝑁𝑂3 − 𝑁𝑖𝑛 = 1200 Kg⁄day 𝑎𝑛𝑑 𝑎𝑠 𝑎𝑠𝑠𝑢𝑚𝑒𝑑 𝑁𝑂3 − 𝑁𝑥 = 5031.2 Kg⁄day 𝑇𝑜𝑡𝑎𝑙 𝑁𝑂3 − 𝑁𝑖𝑛 = 6231.2 Kg⁄day 𝑁𝑂3 − 𝑁 𝑟𝑒𝑚𝑜𝑣𝑒𝑑 𝑖𝑛 𝑎𝑒𝑟𝑎𝑡𝑒𝑑 𝑡𝑎𝑛𝑘 = 0.90 × 6231.2 Kg⁄day = 5608.08 Kg⁄day 𝑁𝑂3 − 𝑁𝐸 = 6231.2 Kg⁄day − 5608.08 Kg⁄day = 623.12 Kg⁄day 𝑁𝑂3 − 𝑁𝑊𝐴𝑆 = 623.12 Kg⁄day 𝑁𝑂3 − 𝑁𝑅 = 623.12 Kg⁄day
Page | 76
VIII.
Phosphorus Balance on the membrane skid
Overall Balance: [𝑇𝑜𝑡𝑎𝑙 𝑃ℎ𝑜𝑠𝑝ℎ𝑜𝑟𝑢𝑠 𝐸𝑛𝑡𝑒𝑟𝑖𝑛𝑔 𝑡ℎ𝑒 𝑠𝑦𝑠𝑡𝑒𝑚] = [𝑃ℎ𝑜𝑠𝑝ℎ𝑜𝑟𝑢𝑠 𝑙𝑒𝑎𝑣𝑖𝑛𝑔 𝑡ℎ𝑒 𝑠𝑦𝑠𝑡𝑒𝑚] + [𝑇𝑜𝑡𝑎𝑙 𝑃ℎ𝑜𝑠𝑝ℎ𝑜𝑟𝑢𝑠 𝑝𝑟𝑒𝑠𝑒𝑛𝑡 𝑖𝑛 𝑊𝐴𝑆] 𝑃𝑖𝑛 = 70 Kg⁄day = 1 g⁄m3 Assuming Efficiency of Phosphorus Removal is 65% 𝑃ℎ𝑜𝑠𝑝ℎ𝑜𝑟𝑢𝑠 𝑟𝑒𝑚𝑜𝑣𝑒𝑑 𝑖𝑛 𝑎𝑒𝑟𝑎𝑡𝑒𝑑 𝑡𝑎𝑛𝑘 = 65% × 70 Kg⁄day = 45.5 Kg⁄day = 0.65 g⁄m3 𝑃𝐸 = 70 Kg⁄day − 45.5 Kg⁄day = 24.5 Kg⁄day 𝑃𝑊𝐴𝑆 = 24.5 Kg⁄day 𝑃𝑅 = 24.5 Kg⁄day 3.2
Energy Balance
Heat transfer during cooling Biogas is a mixture of CO2, N2, O2, H2S and CH4, and with mole fraction of 0.258, 0.034, 0.005, 0.003 and 0.700 respectively. Assuming a steady flow process, the biogas is cooled from 308 to 293 K at a constant pressure of 0.102 MPa. Hence the heat transfer during the process will be evaluated as follows.
Page | 77
Additional assumptions This is steady-flow process since there is no change with time at any point and thus ∆mcv; change in mass of control volume and ∆Ecv; change in energy is equal to zero. The kinetic and potential energy changes are negligible. ∆mcv = ∆Ecv = 0 Analysis of system The cooler is considered as control volume since mass crosses the system boundary during the process. We will note that heat is transferred out of the system.
Furthermore while analyzing the critical properties of the various gases, we can notice that the O2, N2 and CH4 will remain above their critical temperature, but they are all below their critical pressures, and thus we can assume that the biogas behaves as an ideal gas and can be demonstrated using Kay’s rule (Boles et al., 2011) (refer to appendix Energy Balance to demonstrate that biogas can be considered as ideal gas via Kay’s rule).
36Table 3.1: Enthalpy of different gas components
The energy balance for this steady-flow system can be expressed on a unit mole basis as:
Page | 78
eout - eout = ∆esystem = 0 ein = eout → h1 = h2 + qout q”out = h1 – h2 (fore ideal gas) Where: ein= energy input, KJ eout = energy output, KJ ∆esystem = energy change of system, KJ h1 = enthalpy at initial temperature, KJ/Kmol h2 = enthalpy at final tempearature, KJ/Kmol q”out = heat transferred, KJ/Kmol q”out = h1 – h2 = yN2(h1 – h2) + yCO2 (h1 – h2) + yO2(h1 – h2) + yH2S(h1 – h2) + yCH4(h1 – h2) q”out = 0.034(8955.8-8520.88) + 0.258(9731.2-9175.88) + 0.005(8971-8532.63) + 0.003(8959.52-8468.63) + 0.7(6552.37-6363.84) Total mole of biagas = 307.517 kmol Total q”out = 91.7 GJ/day Chapter 4:
Mechanical sketches and schedules
Page | 79
3.33m
8m
A
A
3.38 m
2.25
University of Mauritius
Sketch of Top, Front & Side view of AIP oil-water separator
Beng(Hons) Chemical & Environmental Engineering(Level 3) Project Coordinator: Mr.A.K Ragen & Mr A.Mudhoo Project Supervisor: Mr A.Mudhoo
Design Project 2(CHE4101) Date: 01.04.15 Scale: Not to Scale
Size: A3
Drawn By:
SOOMAREE KESHAV
Group: 3A
ID:
1114132
Page | 80
88 m
42.5 m
Front View
Side view
University of Mauritius
The membrane bioreactor
Beng(Hons) Chemical & Environmental Engineering(Level 3) Project Coordinator: Mr.A.K Ragen & Mr A.Mudhoo
Project Supervisor: Mr A.Mudhoo
Design Project 2(CHE4101) Date: 01.04.15
Scale: Not to Scale
Size: A3
Drawn By:
SOOMAREE KESHAV
Group: 3A
ID:
1114132
Page | 81
University of Mauritius
Sketch of Top, Front & Side view of AIP oil-water separator
Beng(Hons) Chemical & Environmental Engineering(Level 3) Project Coordinator: Mr.A.K Ragen & Mr A.Mudhoo Project Supervisor: Mr A.Mudhoo
Design Project 2(CHE4101) Date: 29.03.15 Scale: Not to Scale
Size: A3
Drawn By:
SOOMAREE KESHAV
Group: 3A
ID:
1114132
Page | 82
University of Mauritius
Sketch of module membrane showing two distinct membranes
Beng(Hons) Chemical & Environmental Engineering(Level 3) Project Coordinator: Mr.A.K Ragen & Mr A.Mudhoo
Project Supervisor: Mr A.Mudhoo
Design Project 2(CHE4101) Date: 29.03.15
Scale: Not to Scale
Size: A3
Drawn By:
SOOMAREE KESHAV
Group: 3A
ID:
1114132
Page | 83
Chapter 5: 5.1
Material of Construction Material of construction for the membrane Bio-reactor Tank
The two possible construction materials for the MBR was be either steel or concrete. However the use of steel is deem to be more expensive and may require more frequent maintenance that a concrete basin. Furthermore while examining the volume of water to be handled by the tank and the subsequent pressure that will be exerted by the fluid which would be relative high; it is recommended to opt for a reinforced concrete structure. Reinforced concrete is ideal for the construction of the basin since the latter is a composite material of steel bars embedded in a hardened concrete matrix; concrete, assisted by steel carries the compressive forces while steel resist tensile forces. In addition concrete is a composite material. The dry mix consists of cement and coarse or fine aggregates. Water is added and this reacts with the cement which hardens and binds the aggregates into the concrete matrix; the concrete matrix sticks and binds on to the reinforcing bars (Choo et al., 1990). 5.2
Material of construction for the module membrane
The specific membrane area (membrane area per unit module volume) refers to the area based on the FS panel. The area per module (FS) or rack (HF) is given in parenthesis, where provided by the supplier. Abbreviations for membrane polymeric materials are: PAN:
polyacrylonitrile
PE:
polyethylene
PES:
polyethylsulphone
PS:
polysulphone
PVDF:
polyvinylidine difluoride
Page | 84
37Table 5.2.1: Membrane configuration definitions
HF or MT
Generic term
FS
Membrane Element
Single sheet, or part there Single filament/fibre or of Panel
tube Module
Multiple element
Module, cassette or stack
Cassette, stack or rack
Multiple multi-element
Train
Train
38Table 5.2.2: Membrane module details of FS
Supplier
Microdyne-Nadir
Membrane or module proprietary name (model) BioCel Membrane material
PES
Pore size (µm) or MWCO (kDa)
150 kDa
Panel dimensions, length x width x depth (mm)
1000 width x 5
Panel area (m2)
10
Membrane separation (mm)
8 (2 mm membrane thickness)
Module dimensions, length x width x depth 1200, 1340 x 650, 1140 x 1800, (mm)
2880
Number of panels per module
-
Total membrane area per module (m2/m3)
70 (90)
Clean water permeability (LMH/bar)
450–550
Supplier
Novasep Orelis
Membrane or module proprietary name (model)
Pleiade®
Membrane material
PAN
Pore size (µm) or MWCO (kDa)
40 kDa
Panel dimensions, length x width x depth (mm)
2610 x 438
Panel area (m2)
2
Page | 85
Membrane separation (mm)
3
Module dimensions, length x width x depth (mm) 2610 x 438 x 1710 Number of panels per module
-
Total membrane area per module (m2/m3)
(36)
Clean water permeability (LMH/bar)
1250 ± 500
Supplier
Toray Industries
Membrane or module proprietary name (model)
Toray (TRM140-100S )
Membrane material
PVDF
Pore size (µm) or MWCO (kDa)
0.08 µm
Panel dimensions, length x width x depth (mm)
1608 x 515 x 13.5 (inc. 6 mm separation)
Panel area (m2)
1.4
Membrane separation (mm)
6
Module dimensions, length x width x depth (mm) 2100 x 810 x 1620 Number of panels per module
50 , 100 or 200
Total membrane area per module (m2/m3)
135
Clean water permeability (LMH/bar)
-
39Table 5.2.3: Membrane module details of HF
Mitsubishi Rayon Engineering
Supplier Membrane
or
module
proprietary
name Sterapore SUR
(model) Membrane material
PE
Pore size (µm) or MWCO (kDa)
0.4 µm
Filament diameter
0.54 mm
Module dimensions, length x width x depth 1035 x 13 x 524 446 (mm) Module area (m2)
Up to 210
Page | 86
Number of filaments per element
-
Cassette dimensions, length x width x depth 1442 x 1538 x 725 (mm) Number of modules per cassette
70
Total membrane area per module (m2/m3)
485
Clean water permeability (LMH/bar)
-
Supplier
Polymem
Membrane or module proprietary name (model) Immem (WW120) Membrane material
PS
Pore size (µm) or MWCO (kDa)
300 kDa; 0.08 µm
Filament diameter
0.7 to 1.4mm
Module dimensions, length x width x depth 1000 to 1500 x 315 (mm) Module area (m2)
60–100m2
Number of filaments per element
a few tens of thousands
Number of modules per rack
Na
Total membrane area per module (m2/m3)
800
Clean water permeability (LMH/bar)
500
For this design the Microdyne-Nadir is chosen made up of polyethylsulphone with a total area of 10000 m2 and with 4 panels of area 10 m2 each having 40 panels per module as per calculation in chapter 2. 5.3
Material of construction for the oil-water separator
The oil-water separator is designed with coalescer plates which operates by method of physical alteration means. The material is of stainless steel. Most other designs utilize a shop-fabricated stainless steel frame or no frame system at all. The standard coalescer plates are typically polypropylene, pvc, or painted carbon steel. Plastic coalescer plates are heat sealed to form the pack and are set in the coalescer frame.
Page | 87
Carbon steel plate coalescer plates are typically stitch welded into the carbon steel coalescer frames and are not removable for cleaning. Coalescer materials that have been used include: polypropylene, pvc, cpvc, acrylic, aluminum, marine aluminum, 304 & 304L stainless steel, 316 and 316L stainless steel. Other materials such as phenolic epoxies composite materials show promise, as well. The coalescer designed in this project is to last the lifetime of the separator unit. The coalescer frame is built of sturdy structural stainless steel. The plate-holding strips are 304 stainless steel, as well. Marine aluminum and 316 stainless steel plate-holding strips are available for particular applications. The Multi-Pack can accommodate any flat plate material. 40Figure 5.3.1: Stainless steel oil-water separator
Page | 88
CHAPTER 6: 6.1
Instrumentation and Control
Control Strategies for the Membrane Bio-reactor Process control and software 1. Feedback control and alarm triggering relies on monitoring of key parameters such as TMP (for indicating membrane fouling condition and triggering a cleaning cycle), DO (for biological process control) and turbidity (for membrane integrity). 2. Unless they are specifically designed to be free from clogging, it is essential that the maintenance schedule includes cleaning of the aerators. This can be achieved by flushing with a dilute hypochlorite solution. For some technologies the aerator flush is scheduled at the same time as the maintenance clean. 3. The principle impact of added process complexity is on the software and programmable logic controllers (PLCs), and on ancillary hardware such as pumps, valves and actuators. For example, intermittent aeration at 10 s means that each valve is actuated pneumatically over 3 million times per year. 4. Foaming control and abatement procedures are particularly important in an MBR since aeration is more intense than for an ASP. Designs should include surface wasting or spraying. 5. Sludge wasting for SRT control can be based on on-line MLSS measurement, although instruments have only recently developed for this. Pre-treatment and residuals management 1. The basic process can be modified in the same way as a conventional ASP to achieve denitrification, chemical phosphorous removal (CPR) and biological nutrient removal (BNR). Additional tanks (or tank volume) and sludge transfer pumps must then be sized accordingly, based on similar bio kinetic principles as those used for the design for the core aerobic process. 2. Pre-clarification can be used to reduce aeration demand (for agitation of
biomass) by reducing solids (“trash”) loading, but this significantly adds to footprint. Upgrading screens is essential, especially for HF iMBRs Grit removal is desirable for plants if no capacity is available to allow the grit to settle out before the membrane tank.
Page | 89
3. MBR sludge is generally less settleable than ASP sludge, with floc sizes generally being smaller and sludge volume index (SVI) values higher. Conventional gravity thickening is therefore less effective for MBR sludge. Membrane thickening can and has been used for this duty, albeit operating at necessarily low fluxes. Tank sizing and redundancy 1. DO levels are _0.5 mg/L in the anoxic zone, typically 1.0–2.5 mg/L in the aerobic zone and relatively high in the membrane region (2–6 mg/L) where aeration is intensive. If recycling for denitrification takes place from the membrane aeration tank to the anoxic zone then the anoxic zone becomes slightly aerobic at the sludge inlets, reducing denitrification efficiency. To compensate for this the anoxic zone must be increased to extend the HRT in this region. Alternatively, sludge can be recycled from the aerobic tank. 2. Retrofitting places additional constraints on design of iMBRs, since the tank size determines the HRT and the shape and placement of immersed membrane modules. Retrofitting of side stream modules, on the other hand, is not constrained by the aeration tank dimensions. 3. Spare capacity is required for membrane cleaning, which either involves draining of the tank and cleaning in air or CIP. In the former case the biomass in the membrane train being cleaned has to be transferred either to a holding tank or to adjacent membrane tanks. In either case sufficient installed capacity is needed to contend with the total volume entering the works while the membrane train is being cleaned. For large plants with a large number of trains (membrane tanks) the cleaning can be sequenced to avoid large hydraulic shocks on the remaining in-service modules. For small plants a buffer tank may be required.
Page | 90
V0
Pressure Sensor (0-4 bar absolute)
V4
F
Mass Flowmeter Permeate
V7
P
T
Feed
Suction Pump (0-4 L/hr)
Membrane Module
F
Massflowmeter
V5
V8
V9
P
V1
BackWash
Retenate
F
Feed/Backwash Pump V6
Pressure Sensor (0-4 bar absolute)
Flow Control
Mass Flowmeter
V2 Chemical Cleaning 1
V3
Chemical Cleaning 2
University of Mauritius
Sketch 1: Cleaning control of MBR
Beng(Hons) Chemical & Environmental Engineering(Level 3)
Project Coordinator: Mr.A.K Ragen & Mr A.Mudhoo Project Supervisor: Mr A.Mudhoo
Design Project 2(CHE4101)
Date: 3.06.15 Scale: Not to Scale
Size: A3
Drawn By:
SOOMAREE KESHAV
Group: 3A
ID:
1114132
Page | 91
4x0.405 l/d Excess Sludge
Concentrated Influent P1 = 0.075 l/min
Air V4
V2
V1
SV 4
V3 Overflow
PS 3
P
Over flow alarm
Tap Water
P2 =
P5 =
0.9 l/min
0.09 l/min (fil) – 0.3 l/min (BW)
PS 4
Degas vessel
P Emergency Overflow pH
Cooler
pH
DO
ORP
Cooler
Cooler
UF Membrane
V7
V6
Effluent grab sample
Over flow alarm
V8
Mixer SV 1
Aerobic/Anoxic zone Anaerobic zone
PS 2
Mixer
P SV 3
P
Permeate Over Flow
PS 1
P3 = 0.375 l/min
P4 = 7.651 l/min
V5 SV 2
University of Mauritius Beng(Hons) Chemical & Environmental Engineering(Level 3) Project Coordinator: Mr.A.K Ragen & Mr A.Mudhoo Project Supervisor: Mr A.Mudhoo
Backwashing Tank (7L)
Air 7.651 l/min
F2
Sketch 2: PID of MBR Date: 25.06.15 Scale: Not to Scale
Design Project 2(CHE4101) Size: A3 Drawn By: Group: 3A ID:
SOOMAREE KESHAV 1114132
Page | 92
Sewer
O2 P2
T
Ph
Computer
Sewer
P3 Peristaltic Pump Membrane
Demi water
Activated Sludge
NaOCl Permeate
Air
Mass Balance Peristaltic Pump Centrifugal Pump
Back Flush Pump
Damper
P1
F
University of Mauritius
Sketch 3: PID of Module membrane
Beng(Hons) Chemical & Environmental Engineering(Level 3) Project Coordinator: Mr.A.K Ragen & Mr A.Mudhoo Project Supervisor: Mr A.Mudhoo
Design Project 2(CHE4101) Date: 3.06.15 Scale: Not to Scale
Size: A3
Drawn By:
SOOMAREE KESHAV
Group: 3A
ID:
1114132
Page | 93
CHAPTER 7: 7.1
Safety Considerations
The oil-water separator
Personal Safety: 1. Toxic substances present in wastewater Deviation: High; Good State/ Bad state Possible causes: 1. Contact with the Wastewater 2. Needle stick injury when removing screenings from a bar screen
Consequences: 1. Chemicals absorbed through skin when in contact with wastewater. 2. Disease can also enter the body through cuts and abrasion Safeguard: Provide hand gloves and stay away from the wastewater Action: Assistance should be provided and immediate actions should be taken in case of Skin Contact 2. Cleaning and Maintenance Deviation: Clean/ Unclean; Good State/ Bad state Possible causes: Screen blockage or clogging Consequences: 1. Efficiency of screens decreases 2. Wastewater unable to pass through causing overflow Safeguard: 1. Two- stage screen in order to facilitate safe cleaning; to reduce the possibility of blockage 2. To allow proper maintenance
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Action: 1. Provide a sensor and an alarm to monitor the risks of blockage 2. Regular checkup and maintenance should be done 7.2
The Membrane Bioreactor
Safety Parameters: Construction and maintenance Deviation: High Possible causes: Safety rules and regulations not properly abided Consequences: 1. Falling into the ponds causing injuries 2. Disease caused by infectious agents like protozoa, virus upon skin contact 3. Chronic poisoning by inhalation Safeguard: 1. Hand railing provided at all places where there is potential of falling around all tanks and other places where falling height is greater than 1.5m 2. Use of life buoys and Safety jackets to get the person out of water Action: Emergency measures should be provided; provide with protective clothing and other personal protective equipment and chemical resistant clothing to avoid exposure of skin
CHAPTER 8: 8.1
Review of the final design
Summary of key Deviations
One of the key deviations for detailed design is that there is a change the initial wastewater flow-rate from 200000 m3/day to 75000 m3/day. The additional deviations and amendments can be noted for the equalization tank design and biogas upgrading system. Furthermore errors were noted in the mass balance of the preliminary design for the biogas upgrading system, the oil and grease separator and coarse screen which lead to several
Page | 95
key mistakes in the preliminary design and had a domino effect in the subsequent calculations, thus it is obvious that while the comparing the mass balance of the preliminary and detailed these variation can be easily noted. Hence to avoid repetitions we shall review mostly the sizing of various equipment. 8.2
Review of API Separator
Preliminary Design
Detailed Design
Cross-sectional area = 54m2
Minimum
Reason/Comments
vertical
cross
sectional area = 60 m²
The key variation is lies in
Depth of channel = 3.38 m
Depth of channel = 3.6 m
these
Length of separator = 3.33 m
Length of separator = 3.33 m
parameters
Width of channel = 8 m
Width of channel = 8 m
Number of channels = 4
Number of channels = 4
Retention time = 30 min
Retention time = 30 min
Construction Material : Steel
Construction material: Stainless steel
Not considered
Rise rate of oil globules 0.263
Not considered
Velocity = 3 ft/min
Not considered
Area of single channel = 14.9 m²
Not considered
8.3
Length of forebay= 14.2 m
Review of the membrane bioreactor
The Reactor Number of tanks
1
Depth (m)
4.4
Length (m)
42.5
Width(m)
88 Fine bubble ceramic diffuser
Aeration system
Oxygen
demand
=
1565.40 𝑚3 𝑜𝑓 𝑂2⁄𝑑𝑎𝑦
Page | 96
Air pipe diameter (m)
0.32
Length of air pipe(m)
30
Power required (KPa)
2.28
Number of centrifugal blowers
1 (+1 as back up)
Inlet pipe
0.164
Effluent pipe Effluent box(m)
0.438 4x3
Aeration period
5.12 Hr
Diffuser submergence(m)
7
Oxygen transfer efficiency (OTE)
35%
Aeration configuration
Covering the floor completely
Air supply SRT
Using a centrifugal blower feeding 7454.24 𝑚3 𝑜𝑓 𝑎𝑖𝑟⁄𝑑𝑎𝑦 10 days
BOD vol. loading F/M
0.938
𝐾𝑔 𝑚3 . 𝑑𝑎𝑦
0.3
The membrane Module Am
9887 m2
Area per element
250 m2
Actual membrane area
10000 m2
Number of elements
40
K’
120 N LMH/bar
Jnet
21 LMH
Jnet,actual
20 LMH
J’net,actual
25 N LMH
J’b
42 N LMH
J’actual
30 N LMH
Page | 97
CHAPTER 9: 9.1
ECONOMICS OF THE PROJECT, AS DESIGNED
Total purchase equipment cost
This represents the basis for estimating the capital investment for a chemical plant. The cost of all the main equipments in the treatment plant, namely, the UV reactors ,the biogas upgrading system, API Separator, and among other ; likewise some equipment cost were estimated by scaling. The Marshall and Swift equipment cost index was used to obtain the present time costs of the equipment. Total purchase equipment cost = Rs. 159,268,246 9.2
Total capital investment (TCI)
This is a very large amount of money that is initially invested before the start of operation of a plant and this is normally used to purchase land and purchase installation of machinery and equipment. As soon as land has been purchased and made available and services must be obtained, the plant is set-up with all the necessary that pilings, controls and services. It should be noted that money will also be needed to pay for expenses incurred for the operation of the plant. The money needed for setting up the plant is known as the Capital Investment. Capital Investment is the total amount of money needed to supply the necessary plant and manufacturing facilities plus the amount of money required as working as working capital and operation of the facilities. Total Capital investment is calculated as: TCI = FCI + WC Where: TCI - Total Capital Investment FCI - Fixed Capital Investment WC - Working Capital This represents the sum of the fixed capital investment and the working capital. Working capital = Rs. 19,582,968 Fixed capital investment is the sum of the direct and indirect costs. The direct cost consists of expenses on the land, the purchased equipment, the instrumentation and controls, the piping and electrical systems, among others while the indirect costs are
Page | 98
expenses which are not directly involved with material and labor of the installation of the plant. 9.3
Total product cost
It represents the sum of the manufacturing cost and the total general expenses. The manufacturing cost is given by the sum of the direct production costs, the fixed charges and the plant overheads. The direct production costs include the costs of raw materials; however for our treatment plant no raw material will be needed, operating labor, laboratory charges and maintenance. Total product cost = Rs. 160, 596,085 The fixed charges are expenses pertaining to depreciation, taxes and insurance. Fixed charges = Rs. 34,812,057 Plant overheads = Rs. 16,059,608 Manufacturing cost = Rs. 138,112,633 The administrative costs, the distribution and selling costs, the research and development costs and interests constitute the general expenses. General expenses = Rs. 22,483,452 Total product cost = Rs. 160,596,085 9.4
Total revenue
For income for the treatment plant will shall consider the sales of treated water for irrigation and the sludge cake for composing. Likewise the treated water and sludge cake will be sold at Rs 0.5/m3 and Rs 25/kg respectively. On a yearly basis, the plant produces 26.65×106 m3of water and 26.44×106 kg of sludge. Thus, Total revenue = Rs. 277, 788,095 9.5
Gross earning cost
This represents the gross profit made by the power plant. It is calculated by the difference of the total income and the total product cost. Gross earning = Rs. 99,613,209
Page | 99
9.6
Pay-back period
Payback can be described as the period of time required for the return on an investment, that is, the time required to recover the initial investment. The simple payback period method is when time value of money is not considered while for the discounted payback method, the time value of money is considered. The payback period indicates whether to go for a specific project or not (Sinnott et al., 2003).
Pay-back period = 7.427 years
9.7
The rate of return
In the case of bank loan, the future return takes the form of interest plus repayment of the principal. This is known as the loan cash flow. While in the case of the fixed asset, the future return takes the form of profits generated by productive use of the asset. This is called project cash flow. Rate of return is also known as Internal Rate of Return, IRR and is the rate at which one is recovering his investment.
This is the rate at which profit is made with respect to the initial investment. The latter would include charges on labour resource. The power plant constitute of 32 personnel. Taking into account all charges and the profit made, Rate of return = 11.4%.
9.8
The Net Present Value (NPV) and Initial Rate of Return (IRR)
The net present value is the harmonization of net cash flows of different period of time at a common time period. The common time period is usually the time the project starts, that is the present time. It is the conversion of future cash flows into present time at a given rate of return. Normally, the net present value of the project is then the difference between the present value of the annual cash flows and the initial required investment.
Page | 100
Present value of the expected cash flows is computed by discounting them at the required rate of return. Net present value is a calculation that compares the amount invested today to the present value of the future cash receipt from the investment. The following parameters are important while calculating NPV: - Rate of return (IRR) - Service life of project or equipment - Annual cash inflow over service life. - Annual cash outflow over service life. - Net cash flows (profits/savings) over service life NPV is the present value of the future cash inflows. NPV= Rs. 1,293,424,747 IRR represents the true interest rate on an investment over the course of its economic life. IRR = 30.45 % 41Table 9.0: Summary of the economics of the treatment power plant
Page | 101
CHAPTER 10:
Environmental Concerns
Even wastewater treatment ensures that not much great demands are been made on the environment and is a step forward towards safeguarding the ecological and marine resources, in particular surf water and ground water and as well as improve sanitation and protect public health. And similarly, the option for wastewater treatment and reuse makes provision for long term water reliability within the community by providing substitute for fresh water and also is a plus-point for water demand and drought management in overall water resources planning; it is be noted that a during the treatment there is a significant amount of waste which is cause for concerns. The table below summaries the various type of waste generated and their related mitigation measure for their resulting nuisance. Waste generated
Source
Treatment of waste/ emissions
Screenings (consisting of Coarse screen
Screenings will be disposed to
large
the landfill without grinding or
debris,
leaves,
plastics,
washing
floatable
Since washing will generate more
materials amongst others)
wastewater thus is not advisable.
Page | 102
Other
alternatives
such
as
incineration may be considered if not too costly. Scum
Activated sludge Scum from the final clarifier are system
scrapped by means of scrappers
Secondary
before
settling tank
discharged to the landfill which
they
are
collected
and
represents a safe, easy and cost effective method of disposal. Sludge in terms of Oil & API grease,
Oil/Water Since oil and grease from API
Separator
COD
cannot sent to land field due to high risk of soil contamination it would trucked to a solid treatment processing plant or send to a processing factor for oil recovery
Sludge
Dry sludge
Primary clarifier
Since the sludge produced have
MBR
considerable amount of BOD.
Secondary
COD and TSS, they will be sent
clarifier
to a digester for stabilization
Drying Bed
Compost plant is the best and most viable mean of disposal
Biogas
Sludge Digester
The biogas is the most valuable waste
Bioreactor
generated, since it has a huge energy potential it will be upgraded and use as fuel of plant’s boilers.
CHAPTER 11:
Conclusion
The aim of this project was to produce a detailed chemical engineering design of a wastewater treatment plant. I was assigned to design the membrane biological reactor
Page | 103
and the Oil-Water separator which required an extensive knowledge of heat & Mass transfer, thermodynamics, Unit operations, wastewater management, chemical process design Chemical economics, Chemical process safety and fluid mechanics. Most of these topics had already been covered during previous years of the undergraduate course and the rest are still ongoing. Indeed, the design also required important decisions to be taken in areas of uncertainty. All the reasoning behind any assumption and decision taken were explained explicitly. To conclude, we can eventually say that there are significant difference in between the primary design and that of the detailed one, especially in terms of sizing and costing. This design project has brought in me many practical skills and knowledge, giving a wider view on the job functions of chemical and environmental engineers.
References 1. Adham, S., DeCarolis, J.F. and Pearce, W. (2004) Optimisation of various MBR systems for water reclamation – phase III, Desalination and Water Purification Research and Development Program Final Report, No. 103. 2. Babcock,
R.
(2005)
www.wrrc.hawaii.edu/research/project_babcock/Babcockmembrane.
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(Accessed March 2015). 3. Benham, B.L., Brannan, K.M., Yagow, G., Zeckoski, R.W., Dillana, T.A., Mostaghimi, S. and Wynn, J.W. (2005) Development of bacteria and benthic total maximum daily loads: a case study, Linville Creek, Virginia. J. Environ. Qual., 34, 1860–1872. 4. Blatchley III, Ernest R., Bastian, K. Chad, Duggirala, Ravi K., Alleman, James E., Moore, Mark, Schuerch, Peter.,1996. “Ultraviolet irradiation and chlorination/dechlorination
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5. Botha, G.R., Sanderson, R.D. and Buckley, C.A. (1992) Brief historical review of membrane development and membrane applications in wastewater treatment in Southern Africa. Wat. Sci. Technol., 25(10), 1–4. 6. C.J. Geankoplis, 1993, Transport Processes and Unit operations, 3rd Edition, India, Prentice Hall Inc 7. Cengel.Y.A , Boles.M.A, 2010, Thermodynamics An Engineering Approach, 7th Edition, New York, Mc Graw Hill. 8. DAR LIN, S.D.L., 2007. Water and Wastewater Calculations Manual. 2nd. New York: McGraw- Hill Companies, Inc. 9. Dieter Deublein and Angelika Steinhauser, 2008, Biogas from Waste and Renewable Resources An introduction 1st edition WILEY-VCH Verlag GmbH & Co. KGaA 10. Digest
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energy
and
water
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2011
available
at:
http://www.gov.mu/portal/goc/cso/report/natacc/DigestEnergy.pdf
,
accessed on 3 Jan 2013 11. DiGiano, F.A., Andreottola, G., Adham, S., Buckley, C., Cornel, P., Daigger, G.T., Fane, A.G., Galil, N., Jacangelo, J., Alfieri, P., Rittmann, B.E., Rozzi, A., Stephenson, T. and Ujang, Z. (2004) Safe water for everyone: membrane bioreactor technology. www.scienceinafrica.co.za/2004/june/membrane.htm 12. Frost and Sullivan (2003) MBR: A buoyant reaction in Europe, Report, June 2003, Frost and Sullivan. 13. Frost and Sullivan (2005) European report: introduction and executive summary, Report, August 2005, Frost and Sullivan. 14. G.Tchobanoglous,F.L.Burton, H.David Stensel, 2004, Metcalf and Eddy Wastewater Engineering Treatment and Reuse, 4th Edition, New York, McGraw Hill. 15. Göbel, A., Thomsen, A., McArdell, C.S., Joss, A. and Giger, W. (2005) Occurrence and sorption behavior of sulfonamides, macrolides and trimethoprim in conventional activated sludge treatment including sorption to sewage sludge. Environ. Sci. Technol., 39, 3981–3989.
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16. Hanzon, B.D and Vigilia, R. “Two Experts Offer Practical Guidance in Designing
and
Operating
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Systems,”
Water
Environment and Technology, November 1999, pp. 35- 42. 17. Ho, Chu-Fei H., Pitt, Paul, Mamais, Daniel, Chiu, Carolyn, and Jolisw, Domenéc.,1998. “Evaluation of UV disinfection systems for large-scale secondary effluent.” Water Environment Research, 70 (6), 11421150. 18. Huber, M.M., Goebel, A., Joss A., Hermann N., Kampmann M., Löffler D., McArdell, C.S., Ried A., Ternes, T.A. and von Gunten, U. (2005) Oxidation of pharmaceuticals during ozonation of municipal wastewater effluents: a pilot study. Environ. Sci. Technol., 39, 4290–4299. 19. J. F. Richardson, J. H. Harker, J. M. Coulson, 1977, “Coulson and Richardson’s CHEMICAL ENGINEERING Fluid flow, Heat transfer and Mass transfer”, Volume 1, 3rd Edition. UK, Pergamon Press 20. J. F. Richardson, J. H. Harker, J. R. Backhurst, 2002, “Coulson and Richardson’s CHEMICAL ENGINEERING Particle, Technology and Separation Processes”, Volume 2, 5th Edition. UK, Elsevier Jaime Benítez, 2009, Principle and Modern Applications of Mass Transfer Operations, 2nd Edition, New Jersey, John Wiley and Sons 21. Joss, A., Andersen, H., Ternes, T., Richle, P.R. and Siegrist, H. (2004) Removal of estrogens in municipal wastewater treatment under aerobic and anaerobic conditions: consequences for plant optimisation. Environ. Sci. Technol., 38(11), 3047–3055. 22. Joss, A., Keller, E., Alder, A., Göbel, A., McArdell, C.S., Ternes, T. and Siegrist, H. (2005) Removal of pharmaceuticals and fragrances in biological wastewater treatment. Water Res., 39(14), 3139–3152. 23. Joss, A., Zabczynski, S., Göbel, A., Hoffmann, B., Löffler, D., McArdell, C.S., Ternes, T.A., Thomsen, A. and Siegrist, H. (2006) Biological degradation of pharmaceuticals in municipal wastewater treatment: proposing a classification scheme. Water Res., 40(8), 1686–1696.
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24. Kennedy, S. and Churchouse, S.J. (2005) Progress in membrane bioreactors: new advances, Proceedings of Water and Wastewater Europe Conference, Milan, June2005. 25. Lawrence, D., Ruiken, C., Piron, D., Kiestra, F. and Schemen, R. (2005) Dutch MBR Development: Reminiscing the Past Five Years, H2O, 36–29. Metcalf, Eddy. (2003) Wastewater Engineering – Treatment and Reuse (3rd edn). McGraw-Hill, New York. 26. Maxwell, S. (2005) the state of the water industry 2005, a concise overview of trends and opportunities in the water business, The Environmental Benchmarker and Strategist Annual Water Issue. 27. Qin, J.-J., Kekre, K.A., Guihe, T., Ooa, M.-H., Wai, M.-N., Lee, T.C., Viswanath, B. and Seah, H. (2005) New option of MBR-RO process for production of NEWater from domestic sewage. J. Membrane Sci. 28. Schyns, P., Petri, C., van Bentem, A. and Kox, L. (2003) MBR Varsseveld, a Demonstration of Progression, H2O, 10–12. 29. Tao, G., Kekre, K., Wei, Z., Lee, T.C., Viswanath, B. and Seah, H. (2005) Membrane bioreactors for water reclamation. Water Sci. Technol., 51(6–7), 431– 440. 30. Ternes, T.A., Joss, A. and Siegrist, H. (2004) Scrutinizing pharmaceuticals and personal care products in wastewater treatment. Environ. Sci. Technol., 38(20), 393A–399A. 31. Van der Roest, H.F., Lawrence, D.P. and van Bentem, A.G.N. (2002) Membrane Bioreactors for Municipal Wastewater Treatment. IWA Publishing. 32. Voet Donald and Voet Judith G., 1995. Biochemistry. 2 Nd ed. New York:John Wiley & Sons, Inc., New York. 33. WEF (2006) Membrane systems for wastewater treatment. Water Environment Foundation, WEFPress/McGraw-Hill, New York. 34. Yang, W., Cicek, N. and Ilg, J. (2006) State-of-the-art of membrane bioreactors: worldwide research and commercial applications in North America. J. Membrane Sci., 270, 201–211.
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Appendices Appendices A: Mass Balance Mass Balance for the MBR
Overall Balance around the MBR Influent = Waste Sludge + Effluent
Q = Influent Flowrate
SE = BOD in Effluent, 𝑚𝑔⁄𝐿
S0 = BOD in influent, 𝑚𝑔⁄𝐿
Hence BOD efficiency can be calculated as follows: Given: BOD in domestic wastewater entering Primary Settling Tank = 307 𝑚𝑔⁄𝐿 Assuming BOD removal efficiency in primary clarifier = 40 % Primary effluent BOD = 307 𝑚𝑔⁄𝐿 × (1 − 0.40) = 184 𝑚𝑔⁄𝐿 Therefore; As assumed permissible limits, that is 40 mg/L = 2800 kg/day is in the effluent
Page | 108
BOD Removal Efficiency in MBR =
184 𝑚𝑔⁄𝐿 −40𝑚𝑔⁄𝐿 184𝑚𝑔⁄𝐿
× 100 = 78%
Hence; 307 𝑚𝑔⁄𝐿 − 40 𝑚𝑔⁄𝐿 𝑂𝑣𝑒𝑟𝑎𝑙𝑙 𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑟𝑦 = ( ) × 100 = 87% 307 𝑚𝑔⁄𝐿 The recycle ratio can be expressed as follows: 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝑅𝑎𝑡𝑖𝑜 =
𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝐹𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑚3 ⁄𝑑𝑎𝑦 𝐼𝑛𝑓𝑙𝑢𝑒𝑛𝑡 𝐹𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑚3 ⁄𝑑𝑎𝑦
Typical recycle ratio for conventional activated sludge process = 0.25 – 0.50 Average Recycle Ratio = 0.375 Therefore; 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝐹𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑄𝑅 = 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝑟𝑎𝑡𝑖𝑜 × 𝐼𝑛𝑓𝑙𝑢𝑒𝑛𝑡 𝑓𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑄0 = 0.375 × 70000 𝑚3 ⁄𝑑𝑎𝑦 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝐹𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 𝑄𝑅 = 26250 𝑚3 ⁄𝑑𝑎𝑦 Also by the methodology of Shu Dar lin (2005), 𝑄𝑅 can be expresses as follows: 𝑄𝑅 =
𝑄0 (𝑥 − 𝑥0 ) 𝑥𝑤 − 𝑥
Whereby: X = MLSS concentration, 2500 𝑚𝑔⁄𝐿 X0 = Primary Effluent TSS, 102.6 𝑚𝑔⁄𝐿 𝑄𝑟 = 𝑟𝑒𝑐𝑦𝑐𝑙𝑒 𝑓𝑙𝑜𝑤𝑟𝑎𝑡𝑒, 26250 𝑚3 ⁄𝑑𝑎𝑦 26250 𝑚3 ⁄𝑑𝑎𝑦 =
70000 𝑚3 ⁄𝑑𝑎𝑦 (2500 𝑔⁄𝑚3 − 102.6 𝑔⁄𝑚3 ) 𝑥𝑤 − 2500 𝑔⁄𝑚3
𝑥𝑤 = 3893.07 𝑔⁄𝑚3 Also; 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝑅𝑎𝑡𝑖𝑜 =
𝑄𝑅 𝑋 = 𝑄0 𝑋𝑅 − 𝑋
Page | 109
Whereby: 𝑋𝑅 is the concentration in recycle sludge and as assumed R is 0.375. 2500 𝑔⁄𝑚3 𝑅𝑒𝑐𝑦𝑐𝑙𝑒 𝑅𝑎𝑡𝑖𝑜 = 𝑋𝑅 − 2500 𝑔⁄𝑚3
Inlet Flowrate:XO = Concentration of TSS in influent Primary Settling Tank Outlet Flowrate:Xe = Concentration of Biomass in effluent Return Sludge: QR = return flow pumping rate, 𝑚3 ⁄𝑑𝑎𝑦 Xu = return microorganism concentration Waste Activated Sludge: QW = Waste flow from recycle waste line, 𝑚3 ⁄𝑑𝑎𝑦 And µ = growth of solids (𝑑𝑎𝑦 −1 ) BOD Balance around MBR 𝐼𝑛𝑝𝑢𝑡 − 𝑜𝑢𝑡𝑝𝑢𝑡 + 𝑔𝑒𝑛𝑒𝑟𝑎𝑡𝑖𝑜𝑛 = 𝑎𝑐𝑐𝑢𝑚𝑢𝑙𝑎𝑡𝑖𝑜𝑛 (𝑄0 𝑆0 + 𝑄𝑅 𝑆𝐸 ) − (𝑄0 + 𝑄𝑅 )𝑆𝐸 −
𝜇𝑋𝑉 𝑑𝑆 = 𝑉 𝑌 𝑑𝑡
𝑑𝑆 𝑉=0 𝑑𝑡 Y = cell yield in kg MLSS/ kg BOD removed At steady state 𝜇𝑋𝑉 = 𝑄0 𝑆0 − 𝑄0 𝑆𝐸 𝑌 𝜇 𝑄0 (𝑆0 − 𝑆𝐸 ) = 𝑓⁄𝑚 𝑟𝑎𝑡𝑖𝑜 = 𝑌 𝑉𝑥 𝑆0 = 184 𝑚𝑔⁄𝐿 Assuming no chemical changes occur: 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝐵𝑂𝐷𝐸 = 40 𝑚𝑔⁄𝐿
Page | 110
Therefore: 𝐵𝑂𝐷𝑅 = 𝐵𝑂𝐷𝑊𝐴𝑆 = 40 𝑚𝑔⁄𝐿 Flow Balance Influent Flow Q0 = 70,000 m3/day Initial BOD = BOD0 = 184 g/m3 As calculated: BOD Efficiency = 78 % BOD in Effluent = 40 g/m3 Solid Balance on membrane 𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑇𝑆𝑆 𝑖𝑛 𝑅𝐴𝑆 = 𝑇𝑆𝑆𝑅 = 𝑋𝑈 𝑔⁄𝑚3 × 𝑄𝑅 𝑚3 ⁄𝑑𝑎𝑦 𝑇𝑆𝑆𝑅 = 10.65 𝑘𝑔⁄𝑚3 × 26250 𝑚3 ⁄𝑑𝑎𝑦 = 279,562.5 𝐾𝑔⁄𝑑𝑎𝑦 𝐴𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑇𝑆𝑆 𝑖𝑛 𝑊𝐴𝑆 = 𝑋𝑢 𝑘𝑔⁄𝑚3 × 𝑄𝑊 𝑚3 ⁄𝑑𝑎𝑦 = 2367.07 𝐾𝑔⁄𝑑𝑎𝑦 Assume TSS Removal Efficiency = 81% Therefore: 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑂𝑓 𝑇𝑆𝑆 𝑖𝑛 𝐸𝑓𝑓𝑙𝑢𝑒𝑛𝑡 = 0.19 × 102.6 𝑚𝑔⁄𝐿 = 19.494 𝑚𝑔⁄𝐿 = 1364.6 𝐾𝑔⁄𝑑𝑎𝑦 Balance on VSS on membrane The removal efficiency of VSS in an MBR system is 90%, therefore; 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝑜𝑓 𝑉𝑆𝑆 𝑖𝑛 𝐸𝑓𝑓𝑙𝑢𝑒𝑛𝑡 = 10% × 82.08 𝑔⁄𝑚3 = 8.208 𝑔⁄𝑚3= 574.6𝐾𝑔⁄𝑑𝑎𝑦 Whereby VSS = 80% TSS = 82.08𝑔⁄𝑚3 =5745.6𝐾𝑔⁄𝑑𝑎𝑦 Assuming: 𝑉𝑆𝑆𝑊𝐴𝑆 = 𝑉𝑆𝑆𝑅 = 5745.6 𝐾𝑔⁄𝑑𝑎𝑦 − 574.6 𝐾𝑔⁄𝑑𝑎𝑦 = 5171.04 𝐾𝑔⁄𝑑𝑎𝑦 NH3-N Balance on the membrane skid Overall Balance: 𝑁𝐻3 − 𝑁𝑖𝑛 = 𝑁𝐻3 − 𝑁𝑜𝑢𝑡
Page | 111
𝑁𝐻3 − 𝑁𝑂𝑈𝑇 = 𝑁𝐻3 − 𝑁𝐸 + 𝑁𝐻3 − 𝑁𝑊𝐴𝑆 By the methodology of N.F.Gray, 2005, the removal efficiency of 𝑁𝐻3 − 𝑁 in an ASP system is 90% 𝑁𝐻3 − 𝑁𝑖𝑛 = 1400 𝐾𝑔⁄𝑑𝑎𝑦 𝑁𝐻3 − 𝑁 𝑟𝑒𝑚𝑜𝑣𝑒𝑑 𝑖𝑛 𝑎𝑒𝑟𝑎𝑡𝑒𝑑 𝑡𝑎𝑛𝑘 = 90% × 1400 𝐾𝑔⁄𝑑𝑎𝑦 = 1260 𝐾𝑔⁄𝑑𝑎𝑦 𝑁𝐻3 − 𝑁𝐸 = 𝑁𝐻3 − 𝑁𝑊𝐴𝑆 = 𝑁𝐻3 − 𝑁𝑅 = 1400 𝐾𝑔⁄𝑑𝑎𝑦 − 1260 𝐾𝑔⁄𝑑𝑎𝑦 = 140 𝐾𝑔⁄𝑑𝑎𝑦 NO3-N Balance on membrane skid Overall Balance: 𝑁𝑂3 − 𝑁𝑖𝑛 = 𝑁𝑂3 − 𝑁𝑜𝑢𝑡 Since nitrification occurs, let 𝑁𝑂3 − 𝑁𝑥 be the amount of nitrates obtained by the nitrification of ammonia. Therefore: 𝑁𝑂3 − 𝑁𝑖𝑛 = 𝑁𝑂3 − 𝑁1 + 𝑁𝑂3 − 𝑁𝑥 Assuming 𝑁𝑂3 − 𝑁𝑥 = 5031.2 Kg⁄day 𝑁𝑂3 − 𝑁𝑜𝑢𝑡 = 𝑁𝑂3 − 𝑁𝐸 + 𝑁𝑂3 − 𝑁𝑊𝐴𝑆 𝑁𝑂3 − 𝑁𝑥 + 𝑁𝑂3 − 𝑁𝑖𝑛 = 𝑁𝑂3 − 𝑁𝐸 + 𝑁𝑂3 − 𝑁𝑊𝐴𝑆 According to N.F.Gray (2005), Removal Efficiency=90% Since 𝑁𝑂3 − 𝑁𝑖𝑛 = 1200 Kg⁄day 𝑎𝑛𝑑 𝑎𝑠 𝑎𝑠𝑠𝑢𝑚𝑒𝑑 𝑁𝑂3 − 𝑁𝑥 = 5031.2 Kg⁄day 𝑇𝑜𝑡𝑎𝑙 𝑁𝑂3 − 𝑁𝑖𝑛 = 6231.2 Kg⁄day 𝑁𝑂3 − 𝑁 𝑟𝑒𝑚𝑜𝑣𝑒𝑑 𝑖𝑛 𝑎𝑒𝑟𝑎𝑡𝑒𝑑 𝑡𝑎𝑛𝑘 = 0.90 × 6231.2 Kg⁄day = 5608.08 Kg⁄day 𝑁𝑂3 − 𝑁𝐸 = 6231.2 Kg⁄day − 5608.08 Kg⁄day = 623.12 Kg⁄day 𝑁𝑂3 − 𝑁𝑊𝐴𝑆 = 623.12 Kg⁄day 𝑁𝑂3 − 𝑁𝑅 = 623.12 Kg⁄day
Page | 112
Phosphorus Balance on the membrane skid Overall Balance: [𝑇𝑜𝑡𝑎𝑙 𝑃ℎ𝑜𝑠𝑝ℎ𝑜𝑟𝑢𝑠 𝐸𝑛𝑡𝑒𝑟𝑖𝑛𝑔 𝑡ℎ𝑒 𝑠𝑦𝑠𝑡𝑒𝑚] = [𝑃ℎ𝑜𝑠𝑝ℎ𝑜𝑟𝑢𝑠 𝑙𝑒𝑎𝑣𝑖𝑛𝑔 𝑡ℎ𝑒 𝑠𝑦𝑠𝑡𝑒𝑚] + [𝑇𝑜𝑡𝑎𝑙 𝑃ℎ𝑜𝑠𝑝ℎ𝑜𝑟𝑢𝑠 𝑝𝑟𝑒𝑠𝑒𝑛𝑡 𝑖𝑛 𝑊𝐴𝑆] 𝑃𝑖𝑛 = 70 Kg⁄day = 1 g⁄m3 Assuming Efficiency of Phosphorus Removal is 65% 𝑃ℎ𝑜𝑠𝑝ℎ𝑜𝑟𝑢𝑠 𝑟𝑒𝑚𝑜𝑣𝑒𝑑 𝑖𝑛 𝑎𝑒𝑟𝑎𝑡𝑒𝑑 𝑡𝑎𝑛𝑘 = 65% × 70 Kg⁄day = 45.5 Kg⁄day = 0.65 g⁄m3 𝑃𝐸 = 70 Kg⁄day − 45.5 Kg⁄day = 24.5 Kg⁄day 𝑃𝑊𝐴𝑆 = 24.5 Kg⁄day 𝑃𝑅 = 24.5 Kg⁄day
Appendix B: Energy Balances Power requirement for the Membrane Bioreactor In order to meet the oxygen demand in the aeration tanks, diffusers are placed and these diffusers require energy. Energy Balance on Aeration Tank Normally the newer technology include centrifugal blowers or positive displacement blowers, since positive displacement blowers is limited to only 425 m3/min volumetric flow rate and centrifugal blowers can be used for volumetric flow rate beyond 80 m3/min, a centrifugal pump is preferred in this case. By the methodology of Frank R. Spellman (2013), the power requirement for aeration is calculated as follows: Average power required for aeration = Pav =
QxRxT x [(Pdis /P) 0.283– 1] 3600 x 29.7 x 0.283 x η
Whereby:
Page | 113
P is the atmospheric pressure Q is the air flow rate T is the inlet temperature in Kelvin (280C = 301.15 K) η is the efficiency of the blower which is normally within the range 70%-80% R is the gas constant, 8.314kJmol-1K-1 Pdis = discharge pressure of blower which varies between 1.7 and 2.4 bar for fine bubble diffusers. Therefore: 1,447.22 𝑚3 ⁄𝑚𝑖𝑛 x 8.314 x 301.15 K 2.05 𝑏𝑎𝑟 0.283 Pav = x [( ) – 1] 3600 x 29.7 x 0.283 x0.75 1.01325 𝑏𝑎𝑟 Pav = 35.24 x 24 = 845.76 kWh/d Energy Balance on membrane bio filter Using the equation:𝑇 = 𝑤𝑅 2 Whereby: T is the torque in Kg.m W is the work kg/m R is the radius of the clarifier, m Assuming W = 20 lb/ft, W = 20 x 1.49 = 29.8 kg/m Since Diameter of clarifier = 26m Radius of clarifier, R = 13 m Hence; kg
𝑇 = 29.8 m × 13.02 𝑚2 = 5036.2 𝐾𝑔. 𝑚 = 49,405.12 𝑁𝑚 𝑃𝑜𝑤𝑒𝑟 = 𝑇𝑜𝑟𝑞𝑢𝑒 × 𝐴𝑛𝑔𝑢𝑙𝑎𝑟𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 = 𝑇 ×
𝐿𝑖𝑛𝑒𝑎𝑟𝑆𝑝𝑒𝑒𝑑 𝑟𝑎𝑑𝑖𝑢𝑠
From N.F Gray (2005), the speed of rakes varies between 3-6m/min and taking an average speed; Speed of rake = 4.5m/min = 0.075m/s
Page | 114
𝐴𝑛𝑔𝑢𝑙𝑎𝑟𝑉𝑒𝑙𝑜𝑐𝑖𝑡𝑦 =
Speed of rake 0.075 𝑚⁄𝑠 = = 0.00577 𝑟𝑎𝑑⁄𝑠 𝑟𝑎𝑑𝑖𝑢𝑠 13.0𝑚
Hence: 𝑃𝑜𝑤𝑒𝑟 = 49,405.12 𝑁𝑚 × 0.00577 𝑟𝑎𝑑⁄𝑠 = 285.07 𝑥 24 = 6841.68 𝑊ℎ/𝑑 Since 6 clarifiers are used, overall power requirements= 6841.68 x 6 = 41.05 kWh/d Energy balance on the amount of pumps As illustrated in the process flow diagram, 13 pumps are being used, therefore, the energy required by the pumps are calculated as follows: Number of pumps= 12 centrifugal pumps which operate 24 hours + 1 centrifugal blower which operate only 5.12 hours /day The wattage of the centrifugal pump = 25.1 kW Energy required = (12 × 25.1 x 24hr) kW + (25.1 ×5hr) = 7354.3 kWh/day Energy production from biogas For biogas containing 67% of methane: 1 m3 of biogas
6.7 kWh (FNR, 2009)
Assumption:
Density of biogas is 1.18 kg/m3
Efficiency of CHP plant is 40% Amount of biogas going in the CHP = 7566.7 kg/d Flowrate
of
biogas
1 m3 of biogas
𝑚𝑎𝑠𝑠𝑓𝑙𝑜𝑤𝑟𝑎𝑡𝑒 𝑑𝑒𝑛𝑠𝑖𝑡𝑦
=
7566.7 1.18
=
6412.46
m3/d
6.7 kWh
6412.46 m3 of biogas Efficiency
=
(6412.46 x 6.7) = 42963.48 kWh of
CHP
plant
is
40%
Energy obtained from CHP per day = (42963.48 x 0.4) = 17185.39 kWh/d
Page | 115
Appendix C: SIZING Sizing of the MBR Sludge age or sludge retention time As per methodology, the SRT for a membrane bioreactor tank is typically 5 to15 days so as to achieve efficient achieve BOD & nitrogen removal. Therefore, the average SRT is assumed: 𝑆𝑅𝑇 =
5 + 15 = 10 𝑑𝑎𝑦𝑠 2
Feed to microorganism ratio As the biomass is actively removing the organic substrate in the wastewater, it follows that the BOD loading should be related to the volume of the biomass in the aeration tank (i.e. Sludge Loading) Assume F/M ratio for conventional process = 0.2-0.4 𝐴𝑣𝑒𝑟𝑎𝑔𝑒
𝐹 0.2 + 0.4 𝑟𝑎𝑡𝑖𝑜 = = 0.3 𝑚 2
The lower the f/m ratio, the lower the rate of metabolism and the greater the BOD removal and sludge settleability. However, as removal efficiency increases so does the overall oxygen demand of the system and so the overall cost of BOD removal. F/m ratio is also the rate of BOD or COD applied per unit volume of mixed liquor. From Metcalf and Eddy, 2003; F/M ratio can be expressed as: 𝐹 𝑄0 (𝑆0 − 𝑆𝐸 ) = 𝑀 𝑉𝑥 𝑊ℎ𝑒𝑟𝑒𝑏𝑦: F/M = food to microorganism ratio, 𝐾𝑔𝐵𝑂𝐷⁄𝐾𝑑𝑀𝐿𝑆𝑆, 𝑑𝑎𝑦 𝑄0 = Inlet Flowrate, 𝑚3 ⁄𝑑𝑎𝑦 𝑆0 = Inlet 𝐵𝑂𝐷, 𝑚𝑔⁄𝐿 𝑆𝐸 = 𝑂𝑢𝑡𝑙𝑒𝑡𝐵𝑂𝐷, 𝑚𝑔⁄𝐿 X = Reactor solids, 𝑚𝑔⁄𝐿
Page | 116
V = Volume of Aeration tank, 𝑚3 Total aeration volume and dimensions of the MBR tank From the equation of food to microorganism ratio 𝐹 𝑄0 (𝑆0 − 𝑆𝐸 ) = 𝑀 𝑉𝑥 𝑊ℎ𝑒𝑟𝑒𝑏𝑦: F/M =0.3 𝐾𝑔𝐵𝑂𝐷⁄𝐾𝑑𝑀𝐿𝑆𝑆, 𝑑𝑎𝑦 𝑄0 = 70,000 𝑚3 ⁄𝑑𝑎𝑦 𝑆0 = 200𝑚𝑔⁄𝐿 = 14000 kg/day 𝑆𝐸 = Taking into consideration permissible limits, that is 40 mg/L = 2800 kg/day X = Reactor solids, 𝑚𝑔⁄𝐿 Assuming that the bioreactor have a concentration varying in the range 2000 𝑚𝑔⁄𝐿3000𝑚𝑔⁄𝐿 Hence, an average MLSS concentration is calculated which equals to 2500 𝑚𝑔⁄𝐿 V = Volume of Aeration tank, 𝑚3 (𝐾𝑔𝐵𝑂𝐷) 70,000 𝑚3 ⁄𝑑𝑎𝑦 (200 𝑚𝑔⁄𝐿 − 40 𝑚𝑔⁄𝐿) 0.3 = (𝐾𝑑𝑀𝐿𝑆𝑆, 𝑑𝑎𝑦) 𝑉 × 2500 𝑚𝑔⁄𝐿
𝑉 = 14934 𝑚3 From methodology, range of depth should vary from 4m to 7 m Assuming depth 4 m and width 4.4 m typical length to width ratio for MBR Therefore: Width = 4.4 m Length = 44 m 𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝐴𝑟𝑒𝑎 𝑜𝑓 𝑡ℎ𝑒 𝑡𝑎𝑛𝑘 =
14934 𝑚3 = 3733.33 𝑚2 4𝑚
Page | 117
3733.33 𝑚2 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝐶ℎ𝑎𝑛𝑛𝑒𝑙𝑠 = = 19.28 = 20 𝐶ℎ𝑎𝑛𝑛𝑒𝑙𝑠 4.4 𝑚 × 44𝑚 Therefore: Actual Length =
𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝐴𝑟𝑒𝑎 𝐴𝑐𝑡𝑢𝑎𝑙 𝑤𝑖𝑑𝑡ℎ
=
3733.33 4.4×20
= 42.42 𝑚
Dimensions of one channel = 42.5 m × 4.4m ×4.5 m Total surface area of the Aeration tank = 42.5m × (4.4m × 20) = 3740 𝑚2 Dimensions of the tank = 42.5m × 88 m Aeration Period or Hydraulic Retention time 𝑉 𝑚3 14934 𝐻𝑅𝑇 = = = 0.213 𝑑𝑎𝑦 = 5.12 ℎ𝑜𝑢𝑟𝑠 3 𝑄 𝑚 ⁄𝑑𝑎𝑦 70000 Volumetric BOD loadings The volumetric BOD loading is defined as the ratio of BOD (Kg/day to the Volume (m3). 𝑉𝑜𝑙𝑢𝑚𝑒𝑡𝑟𝑖𝑐 𝐵𝑂𝐷 𝐿𝑜𝑎𝑑𝑖𝑛𝑔 =
𝐵𝑂𝐷, 𝐾𝑔/𝑑𝑎𝑦 13,968.5𝐾𝑔/𝑑𝑎𝑦 𝐾𝑔 = = 0.938 3 3 3 𝑉𝑜𝑙𝑢𝑚𝑒, 𝑚 14934 𝑚 𝑚 . 𝑑𝑎𝑦
Oxygen Requirements
Air requirement = 0.8 Kg/ Kg BOD removed Therefore: 𝐴𝑖𝑟 𝑅𝑒𝑞𝑢𝑖𝑟𝑒𝑚𝑒𝑛𝑡 = 0.8 Kg × 11200 Kg/ day = 8960 Kg / day Also since density of air = 1.202 Kg/𝑚3 Air Requirement =
8960 Kg / day = 7454.24 𝑚3 𝑜𝑓 𝑎𝑖𝑟⁄𝑑𝑎𝑦 1.202 Kg/𝑚3
Assuming 21% of oxygen in air; Oxygen Requirement = 7454.24 𝑚3 𝑜𝑓 𝑎𝑖𝑟⁄𝑑𝑎𝑦 × 0.21 = 1565.40 𝑚3 𝑜𝑓 𝑂2 ⁄𝑑𝑎𝑦 Air supplied per 𝑚3 of wastewater treated
Page | 118
7454.24 𝑚3 𝑜𝑓 𝑎𝑖𝑟⁄𝑑𝑎𝑦 𝐴𝑖𝑟𝑠𝑢𝑝𝑝𝑙𝑖𝑒𝑑 = = 0.106 𝑚3 𝑜𝑓𝑎𝑖𝑟⁄𝑚3 𝑤𝑟𝑠𝑡𝑒𝑤𝑎𝑡𝑒𝑟 3 ⁄ 70000 𝑚 𝑑𝑎𝑦 Oxygen supplied per 𝑚3 of wastewater treated 1565.40 𝑚3 𝑜𝑓 𝑂2⁄𝑑𝑎𝑦 𝑂𝑥𝑦𝑔𝑒𝑛𝑠𝑢𝑝𝑝𝑙𝑖𝑒𝑑 = = 0.022 𝑚3 𝑜𝑓𝑂2⁄𝑚3 𝑤𝑎𝑠𝑡𝑒𝑤𝑎𝑡𝑒𝑟 70000 𝑚3 ⁄𝑑𝑎𝑦 Membrane biological reactor Shape
Rectangular
Total volume
14934 m3
Dimensions (L x B x H)
42.5m × 88 m × 4.4 m
Number Of channels
20 channels
Material
reinforced concrete
Water temperature
280C brought to 200C
Liquid depth
7m Fine bubble ceramic diffuser
Aeration system
Oxygen
demand
=
1565.40 𝑚3 𝑜𝑓 𝑂2⁄𝑑𝑎𝑦 Aeration period
5.12 ℎ𝑜𝑢𝑟𝑠
Diffuser submergence
7m
Oxygen transfer efficiency (OTE)
35%
Aeration configuration
Covering the floor completely
Air supply SRT
Using a centrifugal blower feeding 7454.24 𝑚3 𝑜𝑓 𝑎𝑖𝑟⁄𝑑𝑎𝑦 10 days
Page | 119
BOD vol. loading
0.938
F/M
𝐾𝑔 𝑚3 . 𝑑𝑎𝑦
0.3
Appendix D: Costing Purchased Equipment Table Equipment
Quantity
Price US
Price US $
Supplier
$/ unit Screening Shandong Jinhaosanyang mechanical bar screens
2
13943
27886
Environmental Protection Equipment Co.LTD
Oil and Grease trap (APl) Oil and grease separator Centrifugal grit pump
ORGANIC 1
616552
616552
BIOTECH PVT LTD
3
27.13
81.39
Shijazhuang
An
pump Co.LTD
Coagulation and Flocculation Jiangyin Alum tank
dosing
1
1500
1500
Fine
Chemical Machinery Co.LTD
Mixer
1
150
150
Jiangyin
Fine
Chemical
Page | 120
Machinery Co.LTD Rapid mixing tank Flat-Blade Radial
Flow
Turbine
Shaghai 6
120
720
pump
Metal Co. LTD
Impeller Chemical feed
Special
Shijazhuang 1
100.96
100.96
An
Pump CO.LTD
Flocculation Tank Centrifugal pump
6
866.86
5201.16
6
48500
291000
6
903.89
5423.34
4
2000
8000
2
755721.67
1511443.34
Shijazhuang
An
pump Co.ltd Shijazhuang
An
pump Co.ltd Shijazhuang
An
pump Co.ltd
Equalization tank Centrifugal pumps Primary clarifier Reciprocating
An
pump Co.ltd Shijazhuang
An
pump Co.ltd 6
18266.67
109600
pump Centrifuge+
Shijazhuang
Shijazhuang
An
pump Co.ltd 1
617702.60
617702.60
ancillaries
Shijazhuang
An
pump Co.ltd
Heat exchanger Hangzhou Sante
Shell and tube heat exchanger 3 +
200000
600000
Pharmaceutical Chemical
Page | 121
baffles tubing
and +
Equipment
all
Co.,
Ltd.
inlet and outlet piping Hangzhou Sante Pharmaceutical Diesel boiler
1
700000
700000
Chemical Equipment
Co.,
Ltd. Hangzhou Sante Pharmaceutical Gas boiler
1
90000
90000
Chemical Equipment
Co.,
Ltd. Membrane Bio-reactor + Module Membrane Shandong Jinhaosanyang Bio reactor
1
150550
150550
Environmental Protection Equipment
Co.,
Ltd. Shandong Jinhaosanyang Bio digester
1
4000
4000
Environmental Protection Equipment
Co.,
Ltd. Membrane with membranes
1
69750
69750
Microdyne-Nadir
incorporated
Page | 122
Centrifugal pump Chlorination system Centrifugal pump
3
2000
6000
1
104000
104000
4
2000
8000
Shijazhuang
An
pump Co.ltd
Shijazhuang
An
pump Co.ltd
Biogas treatment Dongtai Dongjiang Biogas cooler
1
7000
7000
Shipping Assembly
Co.,
Ltd. Dongtai Reciprocal with inter-cooling
Dongjiang 1
75000
75000
Shipping Assembly
Co.,
Ltd. Packed Tower
1
175000
175000
www.alibaba.com Zhengzhou
Packing materials
-
9000
9000
Macro
Imp.
&
Exp. Co., Ltd. Taian
Flash Tank
1
450000
450000
Luqiang
Metal Vessel CO LTD Taian
Stripping tower 1
300000
300000
Luqiang
Metal Vessel CO LTD
Double membrane gas 4
2000
8000
holder
Page | 123
Taian Absorber
3
100000
300000
Luqiang
Metal Vessel CO LTD
Sand filter Total
valves
and accessories
1
155000
155000
-
1000000
100000
Total Purchase equipment cost Rs:
159268246
Bar screen Price = $7340 – 20546 Taking an average price = $13943 API For a cross sectional area of 20 m², price was $ 105 000 in 2007 For our design, cross sectional area = 60 m², hence price = (105000 × 60)/20 = $ 315000 The cost of the API separator in 2015 can be obtained by the use of the following formula: Cost of equipment A = Cost of equipment B x [(Capacity of equipment A/Capacity of equipment B)]0.6 This equation is applicable for capacity that are increased by a maximum of 10 times the capacity of the old equipment. Hence cost in 2015 = 315000 × (60/20)0.6 = $ 608952 Cost of equipment a = Cost of equipment b × (Capacity of a ÷ Capacity of b)0.6 Rapid Mixing Tank Flat-Blade Radial Flow Turbine Impeller (Ms Rochelle Colardo – Alibaba.com) Price = US $ 120/unit Chemical Feed Pump (Ms Bella Gao – Alibaba.com)
Page | 124
Capacity = 2 L/s Price = US $ 500/unit Cost of chemical feed pump for capacity 0.139 L/s = 500 × (0.139 ÷ 2)0.6 = US $ 100.96/unit Flocculation Tank Horizontal Paddle Wheels Flocculator (Ms Candice Zhu – Alibaba.com) Price = US $ 150/ unit Centrifugal Pump (Ms Tracy Hu – Alibaba.com) Capacity = 792 m3/h Price = US $ 1000/unit Cost of centrifugal pump for capacity 624.17 m3/h = 1000 × (624.17 ÷ 792)0.6 = US $ 866.86/unit Costing Primary clarifiers Theory: Calculating cost of equipment: 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑜𝑓 𝑒𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡 𝑎
Cost of equipment a = cost of equipment b × (𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑜𝑓 𝑒𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡 𝑏)0.6 where, Equipment a: actual equipment Equipment b: equipment used as reference Calculating present cost of equipment: 𝑖𝑛𝑑𝑒𝑥 𝑣𝑎𝑙𝑢𝑒 𝑎𝑡 𝑝𝑟𝑒𝑠𝑒𝑛𝑡 𝑡𝑖𝑚𝑒
Present cost = original cost (𝑖𝑛𝑑𝑒𝑥 𝑣𝑎𝑙𝑢𝑒 𝑎𝑡 𝑡𝑖𝑚𝑒 𝑜𝑟𝑖𝑔𝑖𝑛𝑎𝑙 cost 𝑤𝑎𝑠 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑) Currency: 1 US Dollar = 36.50 MUR
Page | 125
Cost index values1: Year
Cost Index
2007
525.4
2015
767.2 Cost estimation of Primary Clarifiers and Pumps
Equipment and auxiliary
Quantity
Primary circular clarifier
2
Reciprocating pump
6
Primary Clarifiers The cost of the primary clarifier can be calculated using the formula2 below: 𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑜𝑓 𝑒𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡 𝑎
Cost of equipment a = cost of equipment b × (𝐶𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑜𝑓 𝑒𝑞𝑢𝑖𝑝𝑚𝑒𝑛𝑡 𝑏)0.6 Capacity of equipments in this context will refer to surface area Now, From Rule Thumb in Engineering Practice3, Cost of equipment b (R.Woods, 2007) = $ 130,000 Surface area of equipment b = 100 m2 Surface area of equipment a = 1000 m2 1000
Cost of equipment a = 130,000 × ( 100 )0.6 = $ 517,539.32 𝑖𝑛𝑑𝑒𝑥 𝑣𝑎𝑙𝑢𝑒 𝑎𝑡 𝑝𝑟𝑒𝑠𝑒𝑛𝑡 𝑡𝑖𝑚𝑒
Present cost = original cost (𝑖𝑛𝑑𝑒𝑥 𝑣𝑎𝑙𝑢𝑒 𝑎𝑡 𝑡𝑖𝑚𝑒 𝑜𝑟𝑖𝑔𝑖𝑛𝑎𝑙 cost 𝑤𝑎𝑠 𝑜𝑏𝑡𝑎𝑖𝑛𝑒𝑑) Original cost in 2007: $ 517,539.32
1
Information retrieved from a pdf online at http://www1.eere.energy.gov/bioenergy/pdfs/mypp_nov_2011_appendix_c.pdf , p.C-11 2 3
Plant Design and Economics for Chemical Engineers, 4th Edition, Peters et al, p.169 Rule Thumb in Engineering, D. Woods, p.408
Page | 126
767.2
Present cost in 2015 = 517,539.32 (525.4) = $755,721.67 Therefore, Present cost in MRU of primary circular clarifier in 2015 = 755,721.67 × 36.50 = Rs 27,583,840.96 Total cost of the 2 clarifiers = 2(27,583,840.96) = Rs 55,167,681.91 Pumps The cost of a reciprocating pump in 2007 was $ 12,500 767.2
Present cost of one pump = 12,500(525.4) = $ 18,266.67 Total present cost of pumps = 6 × 18,266.67 = $ 109,600 Cost estimation of Centrifuge The cost of a centrifuge of with an equivalent clarifying area, Ʃ1, of 2650 m2 had a cost of $ 320,000 in 2007. Thus, the cost of our centrifuge with an equivalent area, Ʃ2, of 2909 m2 is calculated. 2909
Cost of centrifuge = 320,000 × (26500)0.6 = $ 338,416 767.2
Present cost of centrifuge = 338,416(525.4) = $494,162.08 Cost of Ancillaries The cost of the centrifuge and its ancillaries represent a share of 60% and 15% respectively in the capital cost (Directorate General Water Engineering Research and Development Division, n.d.). Hence, 494,162.08
Present cost of ancillaries = 0.15×(
0.6
) = $123,540.52
Cost of centrifuge and ancillaries = 494,162.08 + 123,540.52 = $617,702.60 Summary: Equipment
Primary clarifier
Quantity Unit
2
Cost
Cost($)
equipment($)
755,721.67
1,511,443.34
of
Page | 127
Reciprocating pump
6
18,266.67
109,600
Centrifuge+
1
617,702.60
617,702.60
ancillaries
COMPUTING THE TOTAL CAPITAL INVESTMENT
Total direct cost percentage= 325.5 Total indirect cost percentage = 136 Total direct cost = 0.3255 x PEC = 0.3255 X 159 268 246 = RS 523 196 190
Page | 128
Total indirect cost = 0.136 x PEC = 0.136x 159 268 246 = RS 216 604 815 Fixed capital investment (FCI) = direct cost + indirect cost ∴ FCI = 523 196 190 + 216 604 815 = RS 739 801 005 Working capital (WC) = 0.15 TCI Total capital investment (TCI) = FCI + WC TCI = 739 801 005 + 0.15 TCI ∴ TCI = RS 130 553 119 Calculating the total product cost Total product cost = Manufacturing cost + general expenses 1. Manufacturing cost = Direct Product cost + Fixed charges + Plant overhead Cost A. Direct production costs 1. Raw materials No raw materials are necessary hence the cost for raw materials will be zero. 2. Operating labor Available data: St Martin Treatment plant has an overall plant maximum capacity of 69 000 m3 wastewater/day which is approximately similar to the one designed for a max flow of 75 000 m3/day. Hence the amount of personnel running the plant will be taken similar to that of the St Martin treatment plant. One employee will work 9 hours per day and there will be shift system. Note: the salary of each personnel member is taken from PRB, 2003
Page | 129
Page | 130
Manufacturing cost = Direct production cost +Fixed charges + Plant overhead cost Manufacturing cost = 0.33 TPC + 85115925 Computing the general expenses
TPC = Manufacturing cost + general expenses TPC = 0.33 TPC + 85115925 +0.14 TPC ∴ TPC = Rs 160 596 085
Page | 131
Calculations for depreciation cost The straight line method is used to calculate the overall depreciation of the equipment. The fixed % factor is then evaluated by the double declining method. The depreciation of the equipment over the whole service lifetime is calculated by using the declining balance method. Nevertheless, the yearly depreciation of building is assumed to be a % of the building value. 1. Equipment depreciation Straight line method
Available data: V = 159 268 246 Vs = 30 000 USD (taken reference from St Martin treatment plant) n = 25 (taking in consideration all the equipment)
Double declining balance method,
Page | 132
= 159 268 246 ∴ For 1 year, Vs = 159 268 246 /20 = RS 7963412.32 2. Building depreciation Available data: Building cost from the table above= 1 351 011 USD Depreciation on building = 0.025 x Building cost = 955609 ∴ Total depreciation cost = 7963412.32+955609= RS 8919022 Computing the total income Revenue from sale of treated effluent for irrigation purposes The Wastewater Management Authority sells its treated effluent for irrigation at Rs 0.80/m3 and at the Saint Martin Treatment work the treated water is sold at Rs 0.75/m3. In order to compete with them, the treated water will be sold at Rs 0.50 /m3. Total treated water 73012.95 m3/d Revenue = 0.5x 73012.95x 365= Rs 13 324 863 Sale of sludge cake to composting plant
Page | 133
Typical price of compost on the Mauritian market is Rs 25/kg. Since the waste water treatment plant is providing the compost plant with raw material, the dewatered sludge will be sold at Rs 10/kg. Sludge produced = 72 455 kg per day Total revenue from sludge = 72455 x 10 x 365= Rs264 463 232 Total income = 13 324 863 + 264 463 232= Rs277 788 095 Total profit = Total income – Total product cost ∴ Total profit = 277 788 095 -160 596 085= Rs 117 192 010 Computing the gross profit Gross profit = 117 192 010 – 15 % income tax = 117 192 101 – (0.15x 117 192 101) = 99613209 Computing the payback period
Calculating Rate of Return
Calculating Net Present Value (NPV) The net present value, NPV is defined as the difference between the present value of cash inflows and the present value of cash outflows. The NPV is the most straight
Page | 134
forward way of analyzing the profitability of an investment and is sensitive to the reliability of future cash inflows that an investment or project will yield. The NPV is calculated from:
Where:
Page | 135
NPV = ΣV0 – TCI = 2 163 778 870 – 870 354 123 = 1293424747 Calculating Internal Rate of Return (IRR)
Page | 136
For V0 = 12%, the NPV = ΣV0*Annual cash Inflow - Initial Investment = (7.843*264463232) - 870 354 123 = Rs1203867796 For V0 = 20%, the NPV = ΣV0*Annual cash Inflow - Initial Investment = (4.9475*264463232) - 870 354 123 = Rs438100730.9 For V0 = 25%, the NPV = ΣV0*Annual cash Inflow - Initial Investment = (3.9848*264463232) - 870 354 123 = Rs183502349.6 For V0 = 30%, the NPV = ΣV0*Annual cash Inflow - Initial Investment = (3.3286*264463232) - 870 354 123 = Rs9940702 For V0 = 40%, the NPV = ΣV0*Annual cash Inflow - Initial Investment = (2.499*264463232) - 870 354 123 = Rs -209342970.9 Using extrapolation to find the IRR
∴K= 30.45 IRR = 30.45 %
Page | 137
Discounted Payback Period A capital budgeting procedure used to determine the profitability of a project. In contrast to an NPV analysis, which provides the overall value of a project, a discounted payback period gives the number of years it takes to break even from undertaking the initial expenditure. Future cash flows are considered are discounted to time "zero." This procedure is similar to a payback period; however, the payback period only measure how long it take for the initial cash outflow to be paid back, ignoring the time value of money. Initial Investment = Total Capital Investment = RS 870354123 Assumption: Rate, K = 9 % Discounting Factor = (1+K)-n Where; n = number of years
Discounted payback = 4.079 years
Page | 138
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