Tennessee Wastewater Operator Practice Exam

What is the maximum dissolved oxygen (DO) level required for denitrification to occur in an aerobic digester?

1. 0.1 mg/L

2. 0.3 mg/L

3. 0.5 mg/L

4. 0.7 mg/L

The correct answer is: 0.3 mg/L

Denitrification is a critical biological process that converts nitrate or nitrite into nitrogen gas, thereby reducing nitrogen levels in wastewater. For denitrification to occur effectively, the environment must be largely anaerobic, though there can be some tolerance for low levels of dissolved oxygen. The maximum dissolved oxygen level that allows denitrification to proceed without significant competition from aerobic processes is typically around 0.3 mg/L. When dissolved oxygen levels are higher than this threshold, aerobic bacteria will dominate and utilize available oxygen, inhibiting the denitrification process. Therefore, maintaining dissolved oxygen levels at or below 0.3 mg/L in an aerobic digester is essential to promote denitrification while preventing inhibition of this vital process by competing organisms. This understanding is fundamental for wastewater treatment operations aiming to manage nitrogen effectively.