Tennessee Wastewater Operator Practice Exam

One possible cause for high total suspended solids (TSS) concentration in aerobic digester supernatant is?

1. Inadequate mixing

2. Excessive precipitation

3. Denitrification during decanting

4. Low microbial activity

The correct answer is: Denitrification during decanting

High total suspended solids (TSS) concentration in aerobic digester supernatant can be significantly influenced by denitrification processes occurring during decanting. Denitrification is a process where nitrates are reduced to nitrogen gas, often facilitated by certain bacteria in environments with low oxygen levels. When denitrification occurs in the digester, it can lead to the formation of microbial flocs and other particulate matter, contributing to elevated TSS levels in the supernatant. This situation might arise during the decanting phase when the mixing and oxygen conditions can fluctuate, allowing bacteria to thrive in anaerobic conditions, which encourage denitrification. The resulting microbial mass can increase the amount of suspended solids, causing a higher TSS concentration. Inadequate mixing could lead to localized areas in the digester where solids do not fully break down, but it wouldn’t specifically link to the denitrification process or imply a direct increase in TSS during the decanting phase. Similarly, excessive precipitation and low microbial activity may affect solids concentration, but they do not inherently relate to denitrification or explain why TSS would increase specifically during the decanting period. Thus, the connection between denitrification and elevated TSS levels in the super