What is the process by which bacteria convert nitrate and nitrite to nitrogen gas under anoxic conditions?

• A. Nitrification
• B. Denitrification
• C. Anammox
• D. Assimilation

Answer: (B)

Denitrification is the process where bacteria use nitrate and nitrite as electron acceptors in the absence of oxygen, carrying out a stepwise reduction that ends with nitrogen gas released to the atmosphere. This happens in anoxic conditions, which is why it’s the mechanism responsible for converting NO3- and NO2- into N2 in wastewater treatment. Nitrification is the opposite kind of process, aerobic and oxidizing ammonia to nitrate. Anammox also makes nitrogen gas but starts with ammonium and nitrite, not nitrate, so it isn’t about reducing nitrate/nitrite to N2. Assimilation is the uptake of nitrogen into biomass, not a gas-forming process.