Tennessee Wastewater Operator Practice Exam

An aerobic digester is considered sour when the pH falls below which value?

1. 6.0

2. 6.5

3. 7.0

4. 7.5

The correct answer is: 6.5

An aerobic digester is considered sour when the pH falls below 6.5. This pH level indicates an increase in acidity and a potentially unfavorable environment for the microbial processes that are vital for effective digestion. When the pH drops below 6.5, it suggests that there may be an accumulation of volatile fatty acids, which can inhibit the activity of the microorganisms responsible for breaking down organic matter. Maintaining a proper pH range is crucial in aerobic digestion, as a sour condition can lead to reduced digestion efficiency, increased odor problems, and possible system failure. Therefore, the threshold of 6.5 serves as a critical point for operators to monitor and manage to ensure optimal operational conditions in the aerobic digester.