Which biological process primarily occurs in the aeration stage of wastewater treatment?

The biological process that primarily occurs in the aeration stage of wastewater treatment is nitrification. During this stage, air is introduced to the wastewater, providing the oxygen necessary for bacteria to convert ammonia into nitrates. This process is essential for reducing the toxicity of ammonia, which can be harmful to aquatic life if discharged into water bodies.

Nitrification involves two main groups of bacteria: ammonia-oxidizing bacteria (AOB), which convert ammonia (NH3) into nitrite (NO2-), and nitrite-oxidizing bacteria (NOB), which further process nitrite into nitrate (NO3-). This transformation helps to enhance the biological treatment of wastewater, promoting the removal of nitrogen compounds before the effluent is released or further treated.

Other processes listed, such as fermentation and anaerobic digestion, occur under different conditions, typically in anaerobic environments where oxygen is absent. Filtration, while an important part of wastewater treatment, does not involve biological processes and is primarily a physical method for removing suspended solids from the water.