Tennessee Wastewater Operator Practice Exam

What is the maximum expected solids concentration achievable through decanting alone in an aerobic digester?

1. 1.25%

2. 1.50%

3. 1.75%

4. 2.00%

The correct answer is: 1.75%

In an aerobic digester, decanting is a method used to separate the liquid and solid portions of the mixture after digestion. This process relies on the gravity settling of solids, allowing the clearer liquid on top to be removed while retaining settled solids at the bottom. The maximum expected solids concentration achievable through decanting alone typically ranges around 1.75%. This concentration represents a practical limit for what can be obtained under normal operating conditions. At this level, the digester has effectively removed most of the liquid, and the solids remain in a manageable concentration for further processing or disposal. Concentrations higher than this may not be achievable through just decanting due to the potential for increased viscosity, which could hinder further decanting effectiveness and the efficiency of subsequent treatment processes. Thus, 1.75% is recognized as a standard threshold when considering operational limitations and the nature of aerobic digestion handling. In contrast, the other options represent concentrations that are not typically achievable solely through decanting, reflecting either a less concentrated state than what is practically obtained or exceeding operational thresholds and limitations of the anaerobic digestion process.