Design Calculator | No 1
ESTIMATION OF SLUDGE GENERATION–IN BIOLOGICAL TREATMENT PROCESS
(Biokinetics based design approach)
Calculate biological sludge production in activated sludge process
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 SRT based on actual physical plant characteristics and change till the aeration tank size match with the actual site condition
-
Solving the solids generation based on the above SRT, minimum wastewater temperature & at a fixed MLSS concentration
All design specification used were as per 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.
(For detailed process design calculation as the references please refer the Process Design Calculations file submitted with the bid)
Sludge generation based on bio-kinetic model
Firstly, make select SRT and make initial guess for NOx and solve the below equation:
where,
Px,bio = Rate of biomass generation (kg/day)
Q= Influent flow rate
So= Influent bCOD
S= Effluent bCOD desired
SRT= Sludge Retention Time selected
Y= Biomass Yield (Maximum Bacterial Growth Rate / Maximum Substrate Utilization Rate)
fd= fraction of biomass undergoing endogenous decay
kd= Endogenous decay coefficient
NOx= TKN oxidized
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 sales@dynamicequipments.co.in. We will try and help you with your sizing and calculation
INPUT
| Parameter | Value | Unit | Remarks |
|---|---|---|---|
| Flowrate | MLD | ||
| Recirculated flow | % | Typical 3% | Range from 2-5% | May be higher based on wastewater | |
| Average flowrate |
0.01
|
cum/s | |
| 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 | mg/l | Typically in sewage 0.125 | |
| nbVSS | mg/l | Typically in sewage 10% of VSS | |
| Total Kjheldhal 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 | |
| Enter 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 | |
| Temperature (Min) | deg C | As per site condition extreme | |
| Temperature (Max) | deg C | As per site condition extreme | |
| Aeration tank water depth | m | 3-6 meter typically | |
| Treated Sewage Quality Summary | |||
| Biochemical Oxygen Demand, BOD | mg/l | ||
| 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, NH4-N | mg/l | ||
| Design Calculations | |||
| Aeration tank size - BOD removal + Nitrification in Single Stage | |||
| 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 NH4-N (For simplicity non iterative approach is provided herewith, in a regular spreadsheet, it is advised to program for an iterative approach so that the solutions converge) |
| P_X,Bio,VSS | Consists of 3 parts --- Heterotrophic biomass + Non biodegradable VSS in inlfuent + Nitrifier biomass | ||
| Heterotrophic Biomass Solids |
177.98
|
kg/day | |
| Non Biodegradable VSS in influent |
27.284
|
kg/da | |
| Nitrifier Biomass solids |
2.02
|
kg/day | |
| Nox (Based on P_x, Bio) |
5.1300
|
If negative then add the same amount in positive +10 mg/l in TKN input | |
| Solids generation biological, P_X,Bio,VSS |
207.3
|
kg/day | |
| Solids generation VSS, P_X,VSS |
232.3
|
kg/day | |
| Solids generation TSS,P_X,TSS |
318.9 |
kg/day | Sludge production on 100% dry solids basis |
| Net sludge geenration assuming 0.8% solids consistency |
31.89
|
cum/day | @1% 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 |
1062.9
|
kg/day | Wet sludge with 70% w/w moisture content |
| Mass of VSS in aeration tank |
1626.0
|
kg | |
| Mass of TSS in aeration tank |
2232.1
|
kg | |
| Volume of aeration tank |
744
|
cum | |
| Detention time (HRT) |
17.0
|
hours | Based on Plant average flowrate + Recirculated |
| F/M (Food to Microorganisms ratio) |
0.28
|
g BOD/g VSS * d | 0.15-0.25 as per CPHEEO MLVSS=0.8 MLSS |
| Effluent Nitrates (Assumed) |
5
|
mg/l | |
| Oxygen credit (from denitrification) |
0.3718 |
kg/d | IMPORTANT NOTE: Applicable denitrification 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) |
| Summary of result | |||
| Volume of aeration tank |
744
|
cum | |
| Hydraulic retention time |
17
|
hr | |
| F/M ratio |
0.28
|
g BOD/g VSS * d | |
| Hydraulic retention time |
17.0
|
hours | |
| Sludge Generation |
31.89
|
cum/day | @ 1% solids w/w |
