F/M Ratio Calculator
Calculate the food-to-microorganism ratio — a key process control parameter for activated sludge.
Food-to-microorganism ratio
Formula
F/M (day⁻¹) = (Q × S₀) ÷ (V × Xv)
Q = flow, S₀ = influent BOD₅, V = aeration volume, Xv = MLVSS. All mass units cancel; the result is per day.
F/M (day⁻¹) = (Q × S₀) ÷ (V × Xv)
Q = flow, S₀ = influent BOD₅, V = aeration volume, Xv = MLVSS. All mass units cancel; the result is per day.
Typical F/M ranges
| Process | F/M (day⁻¹) |
|---|---|
| Conventional activated sludge | 0.2 – 0.5 |
| Step aeration / contact stabilization | 0.2 – 0.6 |
| Extended aeration | 0.05 – 0.15 |
| High-rate activated sludge | 0.5 – 1.5 |