Tennessee Wastewater Operator Practice Exam

What factor does not affect the concentration of nitrogen in an aerobic digester supernatant?

1. The percentage of primary sludge added

2. Temperature of the digester

3. The duration of the digestion process

4. Retention time in the digester

The correct answer is: The percentage of primary sludge added

The concentration of nitrogen in an aerobic digester supernatant is influenced by several operational factors, including temperature, the duration of the digestion process, and retention time. However, the percentage of primary sludge added does not significantly affect the concentration of nitrogen in the supernatant. In aerobic digestion, nitrogen concentrations are primarily influenced by the microbial activity involved in the breakdown of organic material, which converts nitrogenous compounds into forms that can be utilized or removed. The composition and characteristics of the sludge itself are crucial in determining the nitrogen influx and flow through the system. Thus, once primary sludge is introduced into the digester, the ongoing processes are primarily impacted by the thermodynamic conditions, microbial kinetics, and the time allowed for digestion rather than by the initial percentage of primary sludge. This means that even as the primary sludge content varies, the microbial processes and the retention times dictate how nitrogen is transformed and removed from the supernatant, making the percentage of primary sludge less relevant in this specific context of concentration.