Tennessee Wastewater Operator Practice Exam

What adjustment should be made to the SRT if water temperature drops significantly in an activated sludge process?

1. Decrease the SRT

2. Increase the SRT gradually

3. Keep the SRT constant

4. Purge excess sludge immediately

The correct answer is: Increase the SRT gradually

In an activated sludge process, the Sludge Retention Time (SRT) is crucial for ensuring that the microbial population has sufficient time to break down organic matter. When the water temperature drops significantly, it can negatively impact the activity and metabolism of the microorganisms, as their enzymatic processes are temperature-dependent. Increasing the SRT gradually allows for a longer retention of the microbial population in the system. This is important because a longer SRT can help maintain an adequate concentration of active biomass capable of adapting to the lower temperatures. Sustaining the microbial population is essential, as it ensures that there are enough microorganisms available to manage the treatment effectively, despite their reduced activity levels due to the colder environment. In contrast, decreasing the SRT or keeping it constant may not provide the necessary time for the microorganisms to adapt and could lead to decreased treatment efficiency. Purging excess sludge immediately is typically a response to higher biomass levels, but under high-load conditions with reduced activity, it could further diminish the population of microorganisms that are already stressed due to temperature changes. Thus, when faced with a drop in temperature, increasing the SRT gradually is the most appropriate action to maintain effective treatment and safeguard the health of the microbial community.