Wastewater Treatment Operator Certification Practice Test

What is sludge bulking in an activated sludge process?

1. When mixed liquor solids settle slowly and compact to a limited extent

2. When old sludge denitrify and cause sludge to rise as a result of gastrification

3. When sludge form large aggregates and cause sludge to settle quickly

4. When compaction in the secondary clarifier is improved due to chemical injection

The correct answer is: When mixed liquor solids settle slowly and compact to a limited extent

Sludge bulking in an activated sludge process refers to a condition where the mixed liquor solids, otherwise known as activated sludge, do not settle effectively during the clarification phase. In this scenario, the sludge settles slowly and, as a result, compacts to a limited extent. This can lead to an increased volume of sludge in the clarifier and can negatively impact the overall performance of the wastewater treatment system. This phenomenon often occurs because of the presence of filamentous bacteria or other factors that prevent effective flocculation, thereby impeding proper settling. When sludge bulking is present, it can be challenging to separate the solids from the liquid phase, leading to issues such as elevated effluent turbidity and poor effluent quality. Effective management of these conditions is crucial to maintain optimal function in an activated sludge system. The other options describe different phenomena related to sludge behavior but do not accurately represent sludge bulking in the context of the activated sludge process. For instance, old sludge denitrifying or the enhancement of compaction through chemical injection are crucial considerations but pertain to separate issues in treatment processes.