What is a typical food-to-microorganism (F/M) ratio for conventional activated sludge?

The food-to-microorganism (F/M) ratio is a critical parameter in the design and operation of wastewater treatment systems, particularly in conventional activated sludge processes. It represents the amount of biochemical oxygen demand (BOD) available to microorganisms in relation to the biomass present in the system.

A typical F/M ratio for conventional activated sludge falls within the range of 0.2 to 0.5. This range is considered ideal for achieving effective treatment rates while allowing for optimal growth and maintenance of the microbial population. An F/M ratio within this range ensures that microorganisms have adequate food (BOD) to maintain a healthy level of activity, which is essential for efficiently breaking down organic matter in wastewater.

Ratios lower than this range may indicate insufficient food for the biomass, potentially leading to underperformance in treatment, while significantly higher F/M ratios might result in overloading, which can lead to operational issues such as excessive growth and the washout of microorganisms, negatively impacting treatment efficiency.