Wastewater Treatment Operator Certification Practice Test

What does the "F" in F/M ratio represent?

1. The microorganism population in the aeration tank

2. The amount of filamentous bacteria in the activated sludge process

3. The MLVSS in the aeration tank

4. The food for the microorganisms flowing into the aeration tank, in lbs/day

The correct answer is: The food for the microorganisms flowing into the aeration tank, in lbs/day

The "F" in the F/M ratio stands for the food for the microorganisms, which refers specifically to the organic matter, or influent biochemical oxygen demand (BOD), entering the aeration tank measured in pounds per day. The F/M ratio, therefore, is a critical parameter in the activated sludge process as it compares the amount of food available to the microorganisms to the mass of microorganisms in the aeration tank. This ratio helps operators determine if there is an adequate amount of food for the microorganisms, which directly affects the treatment efficiency. A high F/M ratio indicates that there is more food available relative to the microbes, which could lead to insufficient growth and possibly poor treatment performance. Conversely, a low F/M ratio suggests there are plenty of microorganisms available to process the food, which generally enhances treatment. Understanding this balance is essential for optimizing the wastewater treatment process and maintaining effective microorganism populations for efficient treatment.