For ammonia removal by denitrification, approximately how many pounds of O2 are required?

• A. 0.5
• B. 2.0
• C. 4.6
• D. 6.0

Answer: (C)

The key idea is that removing ammonia through a denitrification process relies on two stages: first nitrification, which uses oxygen to oxidize ammonia to nitrate, and then denitrification, which occurs without oxygen by reducing nitrate to nitrogen gas. The oxygen demand comes from the nitrification step, and the standard stoichiometry shows about 4.57 pounds of O2 are needed to oxidize one pound of ammonia-nitrogen to nitrate. So, for ammonia removal via a denitrification path, you’d supply roughly 4.6 pounds of O2 per pound of ammonia-nitrogen treated. The other numbers don’t match this established oxygen requirement for the nitrification step.