Sewage Treatment Plant Calculator

Model flows, volumes, and treatment efficiency clearly. Review oxygen demand, sludge production, and clarifier sizing. Make informed wastewater design decisions with organized calculation results.

Plant Design Inputs

Number of people connected to the plant.
Liters per capita per day.
Percent added to base sewage flow.
Used to estimate maximum design flow.
mg/L entering the plant.
mg/L leaving the plant.
mg/L entering the plant.
mg/L after treatment.
Hours of flow balancing storage.
Hours in primary settling.
Hours in biological treatment.
Mixed liquor suspended solids, mg/L.
Active biomass fraction of MLSS.
kg BOD per kg MLVSS·day.
kg O₂ per kg BOD removed.
kg sludge per kg BOD removed.
m³/m²·day for peak flow sizing.
Used to split total clarifier area.
Optional MLD for utilization check.
Reset

Example Data Table

Parameter Sample Value Unit Purpose
Population Served 15,000 persons Base hydraulic loading
Per Capita Flow 135 L/capita/day Daily sewage generation rate
Influent BOD 250 mg/L Organic loading estimate
Influent TSS 300 mg/L Solids loading estimate
Aeration Detention 8 hr Biological treatment sizing
Secondary SOR 25 m³/m²·day Clarifier area sizing

Use the sample values above to test the calculator quickly before entering project-specific design data.

Formula Used

1. Average Flow: Average Flow (L/day) = Population × Per Capita Flow × (1 + Infiltration % / 100)

2. Peak Flow: Peak Flow = Average Flow × Peak Factor

3. BOD Load: BOD Load (kg/day) = Flow (m³/day) × BOD (mg/L) ÷ 1000

4. TSS Load: TSS Load (kg/day) = Flow (m³/day) × TSS (mg/L) ÷ 1000

5. Removal Efficiency: Removal (%) = ((Influent − Effluent) ÷ Influent) × 100

6. Tank Volume: Volume (m³) = Flow (m³/day) × Detention Time (hr) ÷ 24

7. F/M Aeration Volume: Volume (m³) = BOD Load ÷ (F/M × MLVSS in kg/m³)

8. Actual HRT: HRT (hr) = Aeration Volume ÷ Average Flow × 24

9. Oxygen Demand: Oxygen (kg/day) = BOD Removed × Oxygen Factor

10. Sludge Production: Sludge (kg/day) = BOD Removed × Sludge Yield

11. Clarifier Area: Area (m²) = Peak Flow (m³/day) ÷ Surface Overflow Rate

How to Use This Calculator

  1. Enter the connected population and expected per capita sewage generation.
  2. Add infiltration percentage and peak factor to capture wet-weather conditions.
  3. Enter influent and target effluent BOD and TSS concentrations.
  4. Provide detention times for equalization, primary clarification, and aeration.
  5. Enter MLSS, MLVSS fraction, and design F/M ratio for biological sizing.
  6. Set oxygen factor, sludge yield, secondary clarifier SOR, and clarifier count.
  7. Press Calculate Plant Design to show results above the form.
  8. Use the CSV and PDF buttons to export the calculated summary.

Frequently Asked Questions

1. What does this sewage treatment plant calculator estimate?

It estimates average flow, peak flow, pollutant loads, detention volumes, aeration sizing, oxygen demand, sludge generation, clarifier area, and total hydraulic retention time for preliminary wastewater plant planning.

2. Is this calculator suitable for final detailed design?

No. It is best for concept design, screening, and quick sizing. Final design must consider local regulations, process selection, temperature, return sludge, nutrient removal, and detailed hydraulic profiles.

3. Why are both HRT and F/M used for aeration sizing?

HRT checks hydraulic residence time, while F/M checks biological loading on active biomass. Using both gives a more balanced aeration estimate and helps avoid undersized tanks.

4. What is a good F/M ratio for activated sludge?

Typical conventional activated sludge systems often use about 0.2 to 0.5 kg BOD per kg MLVSS per day. Actual targets depend on treatment objectives and operating strategy.

5. Why is infiltration included in the flow calculation?

Infiltration and inflow can significantly increase real plant flow, especially during wet weather. Including it improves tank sizing and helps check whether installed capacity remains adequate.

6. What does clarifier SOR mean?

SOR means surface overflow rate. It relates flow to clarifier surface area and is commonly used to size settling tanks so solids can separate effectively.

7. How is sludge production estimated here?

The calculator applies a sludge yield factor to BOD removed. This gives a quick dry solids estimate, but real sludge quantities vary with biology, sludge age, and stabilization method.

8. Can I use this for package plants and municipal plants?

Yes, for preliminary sizing. It works for small package systems and larger municipal concepts, provided the chosen inputs reflect the intended treatment process and operating conditions.

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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.