What is true about the F/M ratio?

The F/M ratio, or food to microorganism ratio, is a critical parameter in the operation of wastewater treatment systems, particularly in activated sludge processes. It is calculated by dividing the mass of biochemical oxygen demand (BOD) entering the system by the mass of the mixed liquor suspended solids (MLSS) in the system.

The reason the volume of the secondary clarifier is not needed to determine the F/M ratio lies in the fact that this calculation is based solely on the concentrations of influent BOD and the biomass in the system, rather than the specific volumes involved in clarifying. The F/M ratio focuses on the relationship between the available food for the microorganisms (substrate) and the amount of microorganisms present to consume that food. Therefore, it effectively provides insight into how efficiently microorganisms can convert organic material into biomass, but it does not require clarifier volumes for its computation.

In contrast, other aspects such as influent flow rates do influence the F/M ratio since variations in flow can change the concentration of influent BOD and subsequently affect the calculations. Likewise, sludge age is more related to other factors in activated sludge processes, specifically about how long the microorganisms remain in the reactor before being removed, which is not directly quantified by