Basic Wastewater Operator Practice Exam

If your activated sludge plant begins to nitrify, what conditions would you expect to decrease?

1. Settling in clarifiers

2. Chlorine demand

3. BOD effluent

4. TSS in effluent

The correct answer is: Settling in clarifiers

Nitrification in an activated sludge plant refers to the biological conversion of ammonia into nitrate by nitrifying bacteria. This process typically requires specific conditions, including adequate aeration, appropriate pH levels, and the presence of sufficient dissolved oxygen. When nitrification occurs, the dynamics of the treatment process can change. One of the effects of nitrification is that it can improve the settling characteristics of the sludge in clarifiers. As ammonia is converted to nitrate, the biological floc (the aggregate masses of bacteria and material) may become more stable, leading to improved settling properties. Therefore, an increase in nitrification often correlates with improved settling in the clarifiers, which would actually decrease the occurrence of settling issues such as floating sludge or sludge washout. In contrast, the correct answer indicates that if nitrification begins in your activated sludge plant, you would expect a decrease in the settling ability in clarifiers, which can indeed be a symptom of a dysfunctional system where nitrification may disrupt the floc structure or introduce changes in the biomass that affect settling negatively. This nuanced understanding of the mathematics and biology at play can help operations staff better manage their systems and quickly address any operational inefficiencies.