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 × (So-S)
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 3-4 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 non-functioning 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 250-450 mg/l | |
| Biochemical Oxygen Demand, BOD | mg/l | Typically in sewage 100-250 mg/l | |
| Total Suspended Solids, TSS | mg/l | Typically in sewage 250-350 mg/l | |
| Voltalite Suspecded Solids, VSS | mg/l | Typically in sewage 200-250 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 40-50 mg/l ; (Note for special case like TKN > 100 mg/l, contact our design engineering team for more accurate process deisgn) | |
| Ammonical Nitorgen, NH4-N | mg/l | Typically in sewage 40-50 mg/l (Note for special case like NH4-N > 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 3-5 days & For BOD + Nitrification use 8-10 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 | mg/l | ||
| Total Suspended Solids, TSS | mg/l | ||
| 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 | 0.15-0.25 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 | deg-C | 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 | 0.25-0.4 | ||
| 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/cum-air | ||
| 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 | |
