WASTEWATER TREATMENT PROCESS DESIGN CALCULATOR  NO 1
Biological process design (Biokinetics approach) for
Modified activated sludge process – Extended aeration for BOD removal only
Objectives:

Calculate size of aeration tank

Calculate sludge production

Calculate F/M ratio

Calculate aeration blower size
Theoretical basis:
Design Philosophy
The design is based on the substrate utilization rate following microbial kinetics (Michaelis – Menten Enzyme Substrate reaction). The approach used in the design was as follows:
 Selection of target SRT
 Solving the solids generation based on the above SRT, minimum wastewater temperature & at a fixed MLSS concentration
 The volume of the aeration reactor is calculated after estimation of solids generation at a fixed MLSS
 After the volume of aeration reactor is determined, Oxygen requirement is calculated based on the standard equation considering the tender specifications
 For sizing denitrification reactor, and for arriving at most optimal reactor sizing equations governing denitrification kinetics are used
 After sixing the denitrification reactor the anaerobic tank is sized by choosing a fixed reactor volume from 0.51 hr HRT
 Solid separation is then design based on the maximum of SOR, SOR at peak flow, SLR and SLR of peak flow and also considering all other specifications as per tender requirements
All design specification used were as per tender document and CPHEEO. In case, if neither CPHEEO nor tender stipulated a specification, standard texts like Metcalf & Eddy, Syed R. Qasim, WEF MOP were used as reference.
Design parameters
Biokinetic parameter at 20 C  

Description  Parameters  Units  COD oxidation  NH4 oxidation  NO2 oxidation 
Maximum Specific Growth rate  µ_max  g bsCOD/g VSS.d  6.00  0.9  1 
Half Velocity Constant  K_s /K_nh4/K_no2  mg/L  8  0.5  0.2 
Synthesis yield  Y  mg VSS/mg substrate  0.45  0.15  0.05 
Specific Endogenous Decay Rate  b  g VSS/g VSS.d  0.12  0.17  0.17 
Fraction of Biomass that remain as cell debris  f_d  unitless  0.15  0.15  0.15 
Half Velocity Constant for Oxygen  K_o2  mg/L  0.2  0.5  0.9 
Temperature correction
Temperature correction coefficients for biokinetic parameters  

Theta value  Units  COD oxidation  NH4 oxidation  NO2 oxidation 
µ_max  unitless  1.07  1.072  1.063 
b  unitless  1.04  1.029  1.029 
K_s /K_nh4 /K_no2  unitless  1  1  1 
Calculator
(Note – all Yellow are user defined value, all white are fixed values,
all green are calculated value, all orange is calculated not to be
shown)
Instructions
Enter values highlighted in the
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are the results
In case of
any invalid result of nonfunctioning of the calculator, please write
to us at urvpatel@swaenviro.com. We will try and help you with your
sizing and calculation
INPUT
Parameter  Value  Unit  Remarks 

Flowrate  MLD  
Recirculated flow  %  Typical 3%  Range from 25%  May be higher based on wastewater  
Average flowrate  0.01  cum/s  
Enter Wastewater characteristics  
Chemical Oxygen Demand, COD  Typically in sewage 250450 mg/l  
Biochemical Oxygen Demand, BOD  Typically in sewage 100250 mg/l  
Total Suspended Solids, TSS  Typically in sewage 250350 mg/l  
Voltalite Suspecded Solids, VSS  Typically in sewage 200250 mg/l  
gram COD per gram of VSS  Typically in sewage 0.125  
nbVSS  mg/l  Typically in sewage 10% of VSS  
Total Kjheldhal Nitrogen, TKN  mg/l  Typically in sewage 4050 mg/l ; (Note for special case like TKN > 100 mg/l, contact our design engineering team for more accurate process deisgn)  
Ammonical Nitorgen, NH4N  mg/l  Typically in sewage 4050 mg/l (Note for special case like NH4N > 100 mg/l, contact our design engineering team for more accurate process deisgn)  
Total Phosphorous, TP  mg/l  Typically in sewage 7.1 mg/l  
Design parameter  
Select SRT  days  Changed based on the nutrient removal req; For BOD removal use 35 days & For BOD + Nitrification use 810 days  
Select X,TSS  mg/l  Change based on process ASP, Extended aeration, MBBR  
Temperature (Min)  deg C  As per site condition extreme  
Temperature (Max)  deg C  As per site condition extreme  
Aeration tank water depth  m  
Treated Sewage Quality Summary  
Biochemical Oxygen Demand, BOD  
Chemical Oxygen Demand, COD  mg/l  
Total Suspended Solids, TSS  mg/l  
Total Nitorgen, TN  mg/l  Organic Nitrogen + Ammonical Nitrogem + Nitrates  
Total Phophorous, TP  mg/l  
Ammonical Nitorgen, NH4N  mg/l  
PART A Tank sizing or HRT , Sludge generation & F/M ratio  
Outlet BOD theoritical  0.284  mg/l  Theoritical based on steady state condition and mass balance as per the SRT 
Initial Guess for Nox  32.00  mg/l  Change value here by iteration till the calculations shows “CONVERGE” Start with intial guess of 80% of NH4N 
P_X,Bio,VSS  Biomass Production  
Heterotrophic Biomass Solids  88.96  kg/day  First iteration 
Non Biodegradable VSS in influent  13.637  kg/day  
Nitrifier Biomass solids  2.02  kg/day  
Nox (Based on P_x, Bio)  17.4500  (If negative then add the same amount in positive +10 mg/l in TKN input)  
Solids generation biological, P_X,Bio,VSS  104.6  kg/day  
Solids generation VSS, P_X,VSS  129.6  kg/day  
Solids generation TSS,P_X,TSS  198.1  kg/day  Sludge production on 100% dry basis 
Net sludge geenration assuming 0.8% solids consistency  24.76  cum/day  @0.8% solids w/w OR 8000 mg/l TSS in Waste acitvated sludge wasted fro clarifier bottom 
Net sludge geenration assuming 30% solids consistency after dewatering  660.3  kg/day  Wet sludge with 70% w/w moisture content 
Mass of VSS in aeration tank  907.3  kg  
Mass of TSS in aeration tank  1386.6  kg  787.991549737191 
Volume of aeration tank  462  cum  RESULT 
Detention time (HRT)  10.8  hours  Based on Plant average flowrate + Recirculated 
F/M (Food to Microorganisms ratio)  0.23  g BOD/g VSS * d  0.150.25 as per CPHEEO MLVSS=0.8 MLSS 
Effluent Nitrates (Assumed)  5  mg/l  
Oxygen credit (from denitrification)  35.607  kg/d  IMPORTANT NOTE: Applicable denidrification is provided in the form of anoxic tank, otherwise zero. For current use case the effluent nitrate level assumed as <5 mg/l  (For calculation of anoxic tank size refer Metclaf & Eddy) 
PART B Blower sizing  
Oxygen demand  263.54  kg/day  
Oxygen credit from Denitrification  30.27  kg/day  85% of the denitrification oxygen credit used 
Oxygen demand  9.72  kg/hr  Considering denitrification 
Calculating SOTR  Standard Oxygen Trasnfer Rate  
Temperature of wastewater  degC  Based on Maximum wastewater temperate in the influent parameter section  
Actual Oxygen Trasfer Rate required, AOTR  9.72  kg/hr  
C, 20 deg cel  mg/l  From saturation table  
C, t deg cel  mg/l  From saturation table and maximum temp of wastewater and salinity  
C, tank  2  mg/l  Required minimum 2 mg/l 
Alpha  Typical value : 0.65  
Beta  Typical value : 0.95  
F  Typical value : 0.9  
Mid depth correction factor  0.250.4  
Depth of diffusers  4.3  
Temp correction  0.70  
Elevation of site  m  As per site elevation from sea level  
Std barometric pressure  0.989  
Saturated DO due to pressure from water column  10.60  
Standard Oxygen Trasnfer Efficiency  40.28  kg/hr  
Trasfer efficiency  fraction  7.5% per meter of water depth as per vendor  
Weight of Oxygen per cum of air  kg O2/cumair  
Efficiency  
Normal Temperature  20  
Temperature of Air  45  
Air Flowrate required in terms of NTP  514.0  Ncum/hr  Normalized @20 deg C 
Total head loss in aeration  
Total head loss in piping  100.0  mm  Typical 100 mm 
Total head loss in in Elbow, Valves, Tee & Meteres  50.0  mm  Typical 100 mm 
Total head loss in blower assembly  100.0  mm  Typical 100 mm 
Head loss in fine bubble diffuser  200.0  mm  Typical 200 mm 
Submergence head  3800.0  mm  200 mm diffuser height 
Head loss due to clogging  212.5  mm  5 % of a+b+c+d 
Total head loss across the pneumatic system  4462.5  mm  Desired blower pressure head required 
Provide  4.5  mm WC  
SELECT BLOWER WITH  
Air Flowrate required  514.0  Ncum/hr  Discharge side capacity @ NTP 
Head  4.47  m  Submergence + Head loss in air piping 
Summary of result  
Volume of aeration tank  462  cum  
Hydraulic retention time  11  hr  
Sludge Generation  24.76  cum/day  
F/M ratio  0.23  g BOD/g VSS * d  
Hydraulic retention time  10.8  hours  
Blower capacity  514.0  Ncum/hr  
Blower head  0.45  kg/cm2 