Tennessee Wastewater Operator Practice Exam

What happens to the sludge age when the Food to Microorganism (F/M) ratio is increased?

1. Increases

2. Decreases

3. Remains constant

4. Fluctuates significantly

The correct answer is: Decreases

When the Food to Microorganism (F/M) ratio is increased, the sludge age decreases. The F/M ratio reflects the amount of food available to the microorganisms in a biological treatment process, typically measured as the mass of biodegradable organic matter (food) relative to the biomass (microorganisms). Increasing the F/M ratio means there is more food available for the existing microorganisms. In a situation where the amount of food increases relative to the amount of microorganisms, it leads to a situation where the microorganisms will consume the available food more rapidly. This means they grow and reproduce quicker and, as a result, the time that the microorganisms remain in the system (sludge age) is reduced, since their population is maintained by shorter retention times due to higher food availability. A decrease in sludge age can have several operational implications. A lower sludge age could lead to lower sedimentation quality and potentially an increase in the washout of microorganisms from the reactor, which could impact the overall efficiency of the wastewater treatment process. Understanding the relationship between the F/M ratio and sludge age is essential for operators in managing and optimizing treatment systems effectively.