Which term describes bacteria converting nitrates to nitrogen gas?

• A. Nitrification
• B. Filtration
• C. Denitrification
• D. Coagulation

Answer: (C)

Denitrification is the microbial process in which bacteria convert nitrates to nitrogen gas under anaerobic conditions. In wastewater treatment, certain bacteria use nitrate (NO3-) as an electron acceptor when oxygen is scarce, successively reducing it to nitrite, nitric oxide, nitrous oxide, and finally nitrogen gas (N2), which escapes to the atmosphere. This step lowers nitrate levels in the treated water, helping prevent downstream eutrophication. Nitrification is the opposite pathway, an aerobic process that oxidizes ammonia to nitrite and then nitrate. Filtration and coagulation are non-biological treatment steps: filtration physically removes suspended solids, while coagulation helps destabilize and remove particles chemically.