Tennessee Wastewater Operator Practice Exam

Using an SRT of 20 days and an achieved VSR of 16%, how should an aerobic digester be classified?

1. Activated sludge process

2. Solids holding tank

3. Digestion tank

4. Clear water tank

The correct answer is: Solids holding tank

To classify the aerobic digester based on an SRT (Sludge Retention Time) of 20 days and a VSR (Volatile Solids Reduction) of 16%, it is important to consider the definitions and characteristics of the various choices. An aerobic digester primarily functions to biologically stabilize the waste sludge by promoting the breakdown of organic solids. In this scenario, the SRT of 20 days suggests that the sludge is being retained for a significant amount of time, allowing for effective microbial action to achieve reduction of volatile solids—an important aspect of sludge stabilization. The VSR of 16% indicates a measurable reduction in volatile solids, which supports the operational efficiency of the aerobic digestion process. The classification as a "solids holding tank" is appropriate because it describes a system where sludge is retained and treated to achieve solid reduction over a defined period, which aligns with the provided SRT and VSR values. This designation emphasizes the retention of solids in the digestion process, leading to stabilization and reduction of the waste. Other options do not fit this scenario: an activated sludge process typically refers to a system where aeration promotes biological treatment of wastewater rather than solely handling solids, a digestion tank wouldn't specifically emphasize the holding aspect, and a