Florida Wastewater Practice Test

How is the F/M ratio calculated?

1. MLVSS lbs. divided by effluent COD lbs.

2. Influent COD lbs. divided by MLVSS lbs.

3. Solids load divided by flow rate

4. Effluent BOD divided by influent BOD

The correct answer is: Influent COD lbs. divided by MLVSS lbs.

The F/M ratio, or Food-to-Microorganism ratio, is an important parameter in wastewater treatment that helps determine the efficiency of the biological treatment process. It is calculated by dividing the influent Chemical Oxygen Demand (COD) by the Mixed Liquor Volatile Suspended Solids (MLVSS). Calculating the F/M ratio this way provides insight into the amount of organic matter (food) available for the microorganisms present in the treatment system. When the influent COD increases relative to the MLVSS concentration, it suggests that there might be more food available than there are microorganisms to consume it, potentially leading to inefficiencies or growth challenges within the system. Conversely, a low F/M ratio indicates that there may be more microorganisms than available food, which could also lead to problems such as washout or insufficient treatment. Understanding and managing the F/M ratio is vital for ensuring optimal biological activity in a treatment process, allowing operators to adjust feeding rates, maintenance processes, and other operational parameters effectively. The other choices do not accurately capture the F/M ratio's intended calculation or significance in wastewater treatment practices. While they may involve relevant concepts in wastewater management, they do not specifically address the relationship between the organic load and the microbial population in