Tennessee Wastewater Operator Practice Exam

In most aerobic digesters, what happens to ammonia?

1. It is released into the atmosphere

2. It is converted to nitrite and nitrate

3. It is retained as ammonium

4. It is converted to organic compounds

The correct answer is: It is converted to nitrite and nitrate

In most aerobic digesters, ammonia is primarily converted to nitrite and nitrate through a process known as nitrification. This process is facilitated by specific groups of bacteria that thrive in aerobic conditions. The first stage involves ammonia being oxidized to nitrite by ammonia-oxidizing bacteria (AOB), followed by the further oxidation of nitrite to nitrate by nitrite-oxidizing bacteria (NOB). This conversion is critical for removing ammonia from the wastewater, as high levels of ammonia can be toxic to aquatic life. By transforming it into nitrite and nitrate, the system reduces the potential environmental impact of the effluent. Additionally, the resultant nitrates can be utilized by plants in the surrounding areas or further processed in denitrification to return nitrogen to the atmosphere as harmless nitrogen gas. In this context, the other options do not align with the normal processes occurring in aerobic digesters. In particular, ammonia is typically not released into the atmosphere or retained as ammonium during the digestion process, as these would not effectively address the removal of nitrogen compounds from wastewater. While organic compounds do play a role in the digestion process, ammonia does not convert directly into them in aerobic systems. Thus, the conversion of ammonia to nitrite and nitrate represents the