Tennessee Wastewater Operator Practice Exam

How much BOD is needed to convert 1 mg/L of nitrate-nitrogen to nitrogen gas?

1. 2 mg/L

2. 3 mg/L

3. 4 mg/L

4. 5 mg/L

The correct answer is: 4 mg/L

To understand the relationship between the biochemical oxygen demand (BOD) and the conversion of nitrate-nitrogen to nitrogen gas, it's essential to recognize what happens during denitrification. The denitrification process involves converting nitrate (NO3-) into nitrogen gas (N2), which requires a specific amount of BOD as a carbon source for the microorganisms involved. For every 1 mg/L of nitrate-nitrogen that undergoes denitrification, approximately 4 mg/L of BOD is typically needed. This is because the microorganisms use BOD as an energy source to carry out the biochemical processes necessary for the reduction of nitrate to nitrogen gas. The stoichiometry of the denitrification process is such that a greater amount of organic carbon (as represented by BOD) is required to effectively complete the reduction compared to the amount of nitrogen being removed. This requirement highlights the importance of ensuring sufficient organic matter is available in wastewater treatment systems to facilitate effective denitrification and prevent any potential build-up of nitrates in the treated effluent. Thus, the correct answer reflects the proportional BOD requirement needed to convert 1 mg/L of nitrate-nitrogen to nitrogen gas effectively.