Tennessee Wastewater Operator Practice Exam

If the solids concentration suddenly decreases in a digester, what might be the reason?

1. Effective mixing

2. Increased nitrification

3. Filamentous growth

4. Slug loading reduction

The correct answer is: Filamentous growth

When solids concentration in a digester suddenly decreases, one likely reason is the presence of filamentous bacteria. Filamentous growth can lead to poor settling and separation of solids in the digester. These filamentous organisms can proliferate under certain conditions, which often results in the formation of a mat or web-like structure that can obstruct the normal settling process of the biomass. This obstruction can contribute to a decrease in the overall solids concentration because the solids are not settling effectively, leading to an apparent reduction in the concentration within the digester. In contrast, effective mixing or slug loading reductions would typically maintain or improve solid concentrations. Increased nitrification may also influence the digestion process but would not directly cause a sudden decrease in solids concentration. Understanding the dynamics of filamentous growth is crucial for managing and optimizing digester performance, making it a significant topic of discussion in the context of wastewater operations.