Work out aeration tank volume instantly with clear inputs, formula shown and shareable results.
Aeration volume follows from the food-to-microorganism ratio: the biomass inventory needed is BOD load divided by F/M, and volume is that inventory divided by the MLVSS concentration. Conventional activated sludge runs F/M of 0.2-0.4 and extended aeration 0.05-0.15, with correspondingly larger tanks.
Biomass inventory
Biomass (kg MLVSS) = BOD load / F:M ratio
Volume
Volume (m3) = biomass x 1000 / MLVSS (mg/L)
Longer sludge age, more complete oxidation, nitrification and a well-mineralised sludge, at the cost of a larger tank and more aeration energy. Very low F/M can cause pin floc and deflocculation.
Only the volatile fraction is active biomass; the rest is inert inorganic material. Using MLSS overstates the active population, particularly where inorganic loading is high.