Texas Wastewater Class B Practice Exam

What can be a result of insufficient dissolved oxygen in an activated sludge system?

1. Increased organic removal

2. Enhanced flocculation

3. Shift of bacteria types

4. Improved settling rates

The correct answer is: Shift of bacteria types

Insufficient dissolved oxygen in an activated sludge system can lead to a shift in the types of bacteria present. This occurs because different types of bacteria have varying oxygen requirements. In conditions where oxygen levels are low, aerobic bacteria, which thrive in oxygen-rich environments, may be outcompeted or inhibited, allowing more anaerobic or facultative bacteria to proliferate. This shift can negatively affect the biological treatment process, compromising the system's efficiency in breaking down organic material. The other options focus on processes that are generally enhanced or improved with sufficient dissolved oxygen. For instance, organic removal is typically more effective when there is adequate oxygen available for aerobic digestion. Enhanced flocculation also relies on optimal oxygen levels to support the growth and activity of floc-forming bacteria, which helps improve the aggregation of particulates. Similarly, improved settling rates are associated with a healthy population of aerobic bacteria, contributing to well-formed flocs that settle efficiently. Thus, the presence of adequate dissolved oxygen is crucial for optimal performance in an activated sludge system.