Nitrification can lead to disinfectant residual decay and result in growth of bacteria and an ______.

• A. Increase in pH
• B. Increase in alkalinity
• C. Reduction in Oxygen
• D. Reduction in Nitrogen

Answer: (C)

Nitrification uses oxygen, so it reduces the amount of dissolved oxygen in the water. The bacteria that oxidize ammonia (to nitrite and then to nitrate) consume oxygen as part of their metabolism. When disinfectant residual also decays under these conditions, the lowered oxygen level allows bacteria to grow more readily.

The other options don’t fit the process: nitrification does not increase pH (it tends to lower pH by consuming alkalinity), nor increase alkalinity (it actually consumes alkalinity), and it doesn’t reduce total nitrogen—ammonia is transformed to nitrite and nitrate rather than being removed as nitrogen.