Tennessee Wastewater Operator Practice Exam

On what type of treatment process do hydraulic flow variations have the greatest impact?

1. Aerated lagoons

2. Activated sludge

3. Trickling filters

4. Reed beds

The correct answer is: Activated sludge

The activated sludge process is particularly sensitive to hydraulic flow variations due to the biological nature of the treatment. In this process, microorganisms are cultivated in a mixed liquor, comprising wastewater and return activated sludge. The microorganisms rely on a steady and appropriate hydraulic flow to maintain their growth and activity, which are critical for breaking down organic matter effectively. Variations in hydraulic flow can disturb the balance and retention time within the aeration tanks, leading to insufficient contact between the microbes and the pollutants. This can result in suboptimal treatment performance, such as reduced removal rates of biochemical oxygen demand (BOD) and ammonia. If the flow increases suddenly, it may dilute the concentration of microorganisms, impairing their ability to treat the wastewater. Conversely, if the flow decreases significantly, it can lead to excessive retention times, causing sludge age to rise and potentially resulting in the growth of filaments or other undesired microorganisms. This sensitivity contrasts with other treatment methods, such as aerated lagoons, trickling filters, or reed beds, where hydraulic variations might be better absorbed or managed without as severe effects on overall treatment efficiency. Hence, in the context of this question, the activated sludge process is indeed the treatment type that experiences the most significant impact from changes in hydraulic flow.