Tennessee Wastewater Operator Practice Exam

At what dissolved oxygen concentration can denitrification be inhibited?

1. 0.1 mg/L

2. 0.3 mg/L

3. 1.0 mg/L

4. 2.5 mg/L

The correct answer is: 0.3 mg/L

Denitrification is a critical biological process in the nitrogen cycle where nitrate is reduced to nitrogen gas, and it typically requires anaerobic or low-oxygen conditions to proceed effectively. High concentrations of dissolved oxygen can inhibit denitrifying bacteria, which thrive in environments with low to moderate oxygen levels. The correct answer, indicating 0.3 mg/L of dissolved oxygen concentration, is significant because it is recognized as a threshold above which denitrification activity may be substantially reduced. Typically, dissolved oxygen concentrations lower than this are conducive to denitrification, as bacteria can more readily use nitrate in the absence of free oxygen. Understanding the balance of oxygen in wastewater treatment systems is crucial, as maintaining too high a concentration of dissolved oxygen can limit the efficiency of denitrification processes, leading to increased nitrates in effluent and potentially adverse environmental impacts.