Tennessee Wastewater Operator Practice Exam

What is the relationship between water temperature and the performance of activated sludge systems in summer?

1. Higher temperatures improve settling

2. Lower temperatures hinder settling

3. Higher temperatures lead to slower settling

4. Temperature does not affect performance

The correct answer is: Higher temperatures lead to slower settling

In activated sludge systems, temperature plays a crucial role in influencing the biological processes that occur within the treatment process. As temperatures rise, particularly during summer months, the activity of microorganisms increases, which can lead to enhanced aerobic digestion and bacterial growth. However, this increase in microbial activity can also create a situation where the floc particles become less dense and may lead to poorer settling characteristics. Higher temperatures can cause the mixed liquor to become more viscous, and the increased kinetic energy might disturb the settling process. This results in slower settling rates that can contribute to issues such as rising sludge and the potential for effluent quality to diminish. Therefore, while warmer temperatures generally promote biological activity, they can paradoxically hinder the settling efficiency of the sludge due to these changes in viscosity and density of the biological mass. Understanding the balance between biochemical activity and settling characteristics is essential for effective operation of activated sludge systems, especially during warmer months when temperatures may exceed optimal ranges for settling.