Tennessee Wastewater Operator Practice Exam

Which conditions must be present for nitrifying bacteria to convert ammonia to nitrate?

1. Aerobic conditions

2. Anoxic conditions

3. Hypoxic conditions

4. Fermentative conditions

The correct answer is: Aerobic conditions

Nitrifying bacteria require aerobic conditions to effectively convert ammonia into nitrate. This process, known as nitrification, involves two key steps: the oxidation of ammonia to nitrite and then the oxidation of nitrite to nitrate. Both of these steps are facilitated by specific groups of aerobic bacteria that thrive only in environments with sufficient oxygen. In aerobic conditions, oxygen is abundant, enabling these bacteria to carry out their metabolic processes efficiently. Ammonia-oxidizing bacteria, such as Nitrosomonas, perform the first step, while nitrite-oxidizing bacteria, such as Nitrobacter, carry out the second step. Without enough oxygen, these bacteria cannot survive or perform nitrification, leading to the accumulation of ammonia and potentially toxic conditions in wastewater systems. Other environmental conditions mentioned, such as anoxic (absence of oxygen), hypoxic (low levels of oxygen), and fermentative conditions, are not suitable for the nitrifying bacteria that are responsible for this crucial conversion of ammonia to nitrate. These conditions would either inhibit their growth or lead to a different type of microbial activity not related to the nitrification process.