Which removal method is commonly used to remove nitrogen from wastewater?

• A. Physical filtration only
• B. Chlorination followed by filtration
• C. Biological nitrification-denitrification
• D. Sedimentation without biological treatment

Answer: (C)

Nitrogen in wastewater is best removed through a biological nitrification-denitrification process, which uses microbes to transform nitrogen in a two-step sequence. In the aerobic phase, nitrifying bacteria convert ammonia into nitrite and then into nitrate. In the subsequent anoxic phase, denitrifying bacteria use the nitrate as an electron acceptor and convert it to nitrogen gas, which escapes to the atmosphere. This two-stage approach directly reduces total nitrogen in the effluent, addressing problems like eutrophication in receiving waters.

Physical filtration removes solids, not dissolved nitrogen compounds. Sedimentation targets settled solids, again leaving dissolved nitrogen behind. Chlorination disinfects but does not remove or reduce nitrogen nutrients, and filtration after chlorination won’t remove dissolved nitrogen either. So these methods don’t effectively lower nitrogen levels.