Tennessee Wastewater Operator Practice Exam

For every 1 mg/L of nitrate nitrogen (NO3-N) converted to nitrogen gas, how much alkalinity is recovered?

1. 2.5 mg/L as Ca CO3

2. 3.57 mg/L as Ca CO3

3. 4.0 mg/L as Ca CO3

4. 5.0 mg/L as Ca CO3

The correct answer is: 3.57 mg/L as Ca CO3

When nitrate nitrogen (NO3-N) is converted to nitrogen gas (N2) through denitrification, a significant biochemical process occurs in wastewater treatment. This process not only reduces the overall nitrogen load but also impacts the alkalinity of the system. The conversion of 1 mg/L of nitrate nitrogen to nitrogen gas results in a recovery of approximately 3.57 mg/L as CaCO3. This recovery is important because it indicates how much alkalinity is restored, which is essential for maintaining the pH balance and overall health of the wastewater treatment process. In the denitrification process, organic matter is oxidized, which then allows for the reduction of nitrate to nitrogen gas. This chemical reaction is accompanied by a corresponding increase in the alkalinity of the treated effluent, which can be expressed in terms of CaCO3. The value of 3.57 mg/L as CaCO3 is derived from well-established empirical data about the stoichiometry of nitrate reductions associated with biological processes in wastewater treatment. Understanding this ratio is crucial for wastewater operators, as it directly affects the treatment efficiency and the chemical balance of the wastewater system. Properly managing alkalinity is essential for optimizing the performance of biological treatment methods, helping to avoid issues such