Tennessee Wastewater Operator Practice Exam

What biochemical reaction occurs in the anaerobic zone of wastewater treatment?

1. Consumption of ammonia

2. Release of phosphorous

3. Reduction of nitrates

4. Oxidation of sulfides

The correct answer is: Release of phosphorous

In the anaerobic zone of wastewater treatment, one of the key biochemical reactions that occurs is the release of phosphorus. This process is primarily facilitated by specific bacteria known as polyphosphate-accumulating organisms (PAOs). In anaerobic conditions, these bacteria take up organic matter and hydrolyze polyphosphate to release phosphorus into the surrounding environment, which can be beneficial for subsequent treatment processes, such as in enhanced biological phosphorus removal (EBPR). This release of phosphorus occurs because, under anaerobic conditions, PAOs utilize organic substrates for energy while simultaneously releasing available phosphorus that they have previously stored in the presence of oxygen. This process allows for a more efficient recovery of phosphorus, minimizing its potential impact on waterways as a pollutant and supporting nutrient management strategies. In contrast to the other options, which involve different biochemical processes more typical in aerobic or anoxic conditions, the release of phosphorus is a defining feature of the anaerobic microbial activity in the wastewater treatment context.