Nitrification is the process that converts ammonia to nitrate via a nitrite intermediate. Which option correctly describes this process?

• A. Converts nitrate to ammonia
• B. Converts ammonia to nitrite via nitrite intermediate
• C. Converts nitrite to nitrate via nitrate intermediate
• D. Converts ammonia to nitrate via nitrite intermediate

Answer: (D)

Nitrification is an aerobic, two-step microbial process that converts ammonia into nitrate, with nitrite acting as the intermediate. In the first step, ammonia (NH3/NH4+) is oxidized to nitrite (NO2−) by ammonia-oxidizing organisms. In the second step, the nitrite is further oxidized to nitrate (NO3−) by nitrite-oxidizing organisms. Because nitrite is produced and then promptly consumed in the same overall pathway, the complete description of nitrification is ammonia to nitrate via nitrite intermediate.

This is why the option describing ammonia being transformed into nitrate through a nitrite intermediary is the best fit. The other descriptions don’t capture the full two-step sequence, or describe the reverse or an incorrect intermediate, which doesn’t match nitrification occurring in wastewater treatment.