Tennessee Wastewater Operator Practice Exam

What is the equivalent amount of dissolved oxygen recovered from the denitrification of 1 mg NO3 N?

1. 1.5 mg/L

2. 2.86 mg/L

3. 3.2 mg/L

4. 4.0 mg/L

The correct answer is: 2.86 mg/L

In the process of denitrification, nitrate (NO3-) is converted to nitrogen gas (N2) by bacteria in anaerobic conditions, and this process consumes oxygen. To determine the equivalent amount of dissolved oxygen recovered from the removal of 1 mg of nitrogen from nitrate (in terms of NO3 N), it is necessary to understand the stoichiometry involved in the denitrification process. The general chemical reaction for denitrification can be summarized as follows: \[ \text{NO}_3^- + \text{Organic Carbon} -> \text{N}_2 + \text{CO}_2 + \text{H}_2\text{O} \] For every 1 mg of nitrate nitrogen (NO3 N) converted, approximately 2.86 mg of dissolved oxygen is required. Thus, when you calculate the equivalent amount of oxygen that can theoretically be recovered from denitrification of 1 mg of NO3 N, you arrive at the value of 2.86 mg/L. This reflects the oxygen demand associated with this biological process and aligns with the principles of nitrogen metabolism in water treatment. Hence, the correct interpretation of the conversion aligns with the stoichiometric coefficients derived from denitrification equations,