WASTEWATER TREATMENT PROCESS DESIGN CALCULATOR  NO 2
Activated sludge process – Blower sizing
(Blower sizing for BOD removal only excluding nitrification demand)
Objectives:

Calculate size of blower for aeration – BOD removal and nitrification

Calculate blower discharge head required

Convert blower size to field condition suction side conditions
Theoretical basis:
Design Philosophy (Courtesy: reprint from CPHEEO manual on wastewater engineering 2013)
Oxygen required in the activated sludge process for the oxidation of as part of the influent organix matter and for the endogenous respiration of the micro organism in the system. The total oxygen requirement of the process may be formulated as follows
where,
f : Ratio of BOD to ultimate BOD
1.42 : Oxygen demand of biomass, g/g
X : Biological sludge produced per day.
X = Q × Yobs × (SoS)
Yobs = Y/(1+Kdx0c)
Where Y is 0.5 and Kd is 0.06
The formula does not allow for nitrification but allows only for carbonaceous BOQ removal. The extra theoretical oxygen requirement for nitrification is 4.56 kg Oxygen per kg Ammonical Nitrogen. The Ammonical nitrogen oxidized to nitrate. The recommended dissolved oxygen concentration in aeration tank is in the range of 2mg/l, below that there is inhibition in biological activity, moreover in case of MBBR systems, the bulk dissolved oxygen requirement to provide for ideal flux in the biofilm might even go upto 34 mg/l if <1 mg/l ammonical nitrogen is required in the effluent
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 Yellow
Green highlights 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  
42.92  cum/hr  
Enter Wastewater characteristics  
Chemical Oxygen Demand, COD  mg/l  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 Kjehaldhal 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  
Depth of aeration tank  m  As per design  
Temperature (Min)  deg C  As per site condition extreme  
Temperature (Max)  deg C  As per site condition extreme  
Treated Sewage Quality Summary  
Biochemical Oxygen Demand, BOD  mg/l  
Chemical Oxygen Demand, COD  
Total Suspended Solids, TSS  
Aeration tank size – BOD removal only  
P_X,Bio,VSS  Biomass Production  
Heterotrophic Biomass Solids  91.69  kg/day  
Non Biodegradable VSS in influent  14.056  kg/day  
Solids generation biological, P_X,Bio,VSS  105.7  kg/day  
Solids generation VSS, P_X,VSS  131.5  kg/day  
Solids generation TSS,P_X,TSS  201.7  kg/day  Sludge production on 100% dry basis 
Net sludge generation assuming 1% solids consistency  20.17  cum/day  @1% solids w/w 
Net sludge generation assuming 30% solids consistency after dewatering  672.2  kg/day  
Mass of VSS in aeration tank  920.5  kg  
Mass of TSS in aeration tank  1411.5  kg  
Volume of aeration tank  471  cum  
Detention time (HRT)  11.0  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 
Aeration requirement  
Oxygen demand  274.30  kg/day  
Oxygen credit from Denitrification  kg/day  Only applicable if denitrifiction is provided in form of anoxic tank (For calculation of anoxic tank size refer Metclaf & Eddy)  
Oxygen demand  6.72  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  6.72  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  27.86  kg/hr  
Trasfer efficiency  0.32  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  
Air Flowrate required in terms of NTP  355.5  Ncum/hr  Normalized @20 deg C 
Total head loss in aeration  
Total head loss in piping  mm  Typical 100 mm  
Total head loss in in Elbow, Valves, Tee & Meteres  mm  Typical 100 mm  
Total head loss in blower assembly  100.0  mm  Typical 100 mm 
Head loss in fine bubble diffuser  mm  Typical 200 mm  
Submergence head  3800.0  mm  200 mm diffuser height 
Head loss due to clogging  215.0  mm  5 % of a+b+c+d 
Total head loss across the pneumatic system  4515.0  mm  Desired blower pressure head required 
Provide  4515.0  mm WC  
SELECT BLOWER WITH  
Air Flowrate required  355.5  Ncum/hr  Discharge side capacity @ NTP 
Head  4.52  m  Submergence + Head loss in air piping 
Summary of result  
Blower capacity  355.5  Ncum/hr  
Blower head  0.45  kg/cm2 