In wastewater systems, what are nitrification and denitrification, and what is their role in nitrogen removal?

• A. Nitrification reduces nitrate to nitrogen gas; denitrification oxidizes ammonia to nitrite.
• B. Nitrification oxidizes ammonia to nitrite and nitrate under aerobic conditions; denitrification reduces nitrate to nitrogen gas under anoxic conditions, removing nitrogen.
• C. Nitrification and denitrification both add nitrogen to water.
• D. Nitrification occurs anaerobically; denitrification occurs aerobically.

Answer: (B)