Wastewater Treatment Operator Certification Practice Test

What is true if the F/M ratio increases?

1. Less DO is required

2. Less BOD is available

3. DO will not be affected by an increase in F/M ratio

4. More DO is needed

The correct answer is: More DO is needed

The statement that if the F/M (Food to Microorganism) ratio increases, more DO (Dissolved Oxygen) is needed, is correct. The F/M ratio is a critical parameter in wastewater treatment, particularly in activated sludge processes. It represents the amount of biodegradable organic material (food) available for the microorganisms (the biomass) to consume. An increase in the F/M ratio indicates that there is more food (BOD - Biochemical Oxygen Demand) available in relation to the amount of microorganisms present. When there is more food relative to the biomass, the microorganisms will consume oxygen at a higher rate to metabolize this increased amount of organic matter. This increased microbial activity necessitates additional DO in the system to support respiration. If adequate dissolved oxygen isn't provided, the efficiency of the treatment process could be compromised, leading to incomplete degradation of the organic materials. Understanding the dynamics of the F/M ratio is essential for maintaining optimal conditions in a wastewater treatment facility, ensuring effective treatment while preventing issues like organic overload and oxygen depletion.