Tennessee Wastewater Operator Practice Exam

What is the minimum dissolved oxygen (D.O.) level that should be maintained in an aerobic digester under loading conditions?

1. 0.5 mg/L

2. 1.0 mg/L

3. 2.0 mg/L

4. 3.0 mg/L

The correct answer is: 1.0 mg/L

Maintaining a minimum dissolved oxygen (D.O.) level of 1.0 mg/L in an aerobic digester is essential for effective biological treatment processes. In aerobic digestion, aerobic microorganisms rely on dissolved oxygen to break down organic matter efficiently. A D.O. level of 1.0 mg/L is considered the minimum threshold that supports the metabolic processes of these microorganisms, enabling them to thrive and adequately process the waste for stabilization. When D.O. levels drop below this threshold, the efficiency of the digestion process can be compromised, leading to incomplete digestion and possible odor issues due to the production of volatile fatty acids. Additionally, if the levels fall too low, it may create conditions that favor anaerobic bacteria, which are not beneficial in an aerobic digester. Consequently, keeping the D.O. at or above 1.0 mg/L ensures that the aerobic microorganisms can effectively carry out their functions, maintaining the overall health and performance of the digester system.