Tennessee Wastewater Operator Practice Exam

How do decreases in temperature generally affect aerobic biological processes in wastewater treatment?

1. Increase biological activity

2. No effect on efficiency

3. Decrease in settling efficiency

4. Increase in sludge production

The correct answer is: Decrease in settling efficiency

Decreases in temperature generally lead to a decrease in the rate of aerobic biological processes in wastewater treatment. Specifically, cooler temperatures reduce the metabolism and activity of microorganisms, which are essential for the breakdown of organic matter in the wastewater. As these microorganisms become less active, their ability to settle out of the treated water may also be affected. In aerobic processes, the effectiveness of biological treatment relies heavily on the microbial community's ability to consume oxygen and degrade pollutants. When temperatures drop, this microbial activity slows down, causing a delay in the treatment process. As a result, sedimentation of biologically treated sludge can become less efficient, as the decreased biological activity often leads to the production of flocculent and less compact sludge. This poor settling can result in higher turbidity in treated water and may even lead to operational challenges in the clarifiers where the settling of sludge occurs. Thus, the relationship between temperature and biological processes highlights why a decrease in temperature can negatively affect the settling efficiency in wastewater treatment systems.