Wastewater Treatment Load Calculator
Calculate pollutant loads (BOD, TSS, Nitrogen, Phosphorus) entering or leaving a wastewater treatment plant based on flow rate and concentration. Results are expressed in kg/day and lbs/day.
mg/L
mg/L
mg/L
mg/L
persons
Formula
Pollutant Load (kg/day) = Q (m³/day) × C (mg/L) × 10⁻³
Where the conversion factor 10⁻³ arises because:
1 mg/L × 1 m³ = 1 mg/L × 1,000 L = 1,000 mg = 1 g = 0.001 kg
Unit conversions used:
- 1 MGD = 3,785.41 m³/day
- 1 m³/day = 1,000 L/day
- 1 kg = 2.20462 lbs
- Per capita load (g/cap/day) = Load (kg/day) × 1,000 / Population
Assumptions & References
- Flow is assumed to be the average daily flow (ADF); peak flows will produce proportionally higher instantaneous loads.
- Concentrations are assumed uniform (fully mixed) across the cross-section at the measurement point.
- Typical raw domestic wastewater: BOD₅ 150–300 mg/L, TSS 150–300 mg/L, TN 25–60 mg/L, TP 4–12 mg/L (Metcalf & Eddy, Wastewater Engineering, 5th ed.).
- Typical per capita BOD₅ contribution: 45–54 g/cap/day (US EPA, Design Manual: Municipal Wastewater Stabilization Ponds, 1983).
- Typical per capita flow: 200–400 L/cap/day for developed nations (WHO/UNICEF).
- BOD₅ is the 5-day biochemical oxygen demand measured at 20 °C.
- TSS = Total Suspended Solids; TN = Total Nitrogen; TP = Total Phosphorus.
- Reference: Metcalf & Eddy / AECOM, Wastewater Engineering: Treatment and Resource Recovery, 5th ed., McGraw-Hill, 2014.