Tennessee Wastewater Operator Practice Exam

Cycling an aerobic digester between aerobic and anoxic conditions primarily serves to?

1. Increase pH levels

2. Lowers nitrate concentrations

3. Maintain solids concentration

4. Enhance microbial activity

The correct answer is: Lowers nitrate concentrations

Cycling an aerobic digester between aerobic and anoxic conditions primarily serves to lower nitrate concentrations. This process is crucial in wastewater treatment, particularly within the context of nitrogen removal. When oxygen is present in aerobic conditions, nitrifying bacteria convert ammonia to nitrate. However, when the system transitions to anoxic conditions—where oxygen is absent but nitrates can still be used—denitrifying bacteria can utilize the nitrates as a hydrogen source, converting them to nitrogen gas (N2), which is released harmlessly into the atmosphere. This step effectively removes nitrate from the system, contributing to nutrient reduction in effluent and minimizing the risk of eutrophication in receiving waters. Understanding this process is key for operators managing wastewater systems, as maintaining appropriate redox conditions within the digester can significantly impact the efficiency of nitrogen removal and overall plant performance.