Tennessee Wastewater Operator Practice Exam

How does a decrease in water temperature affect aerobic biological processes?

1. Increases solids settling efficiency

2. Decreases oxygen levels

3. Decreases solids settling efficiency

4. Improves gas exchange

The correct answer is: Decreases solids settling efficiency

A decrease in water temperature affects aerobic biological processes by slowing down the metabolic rates of the microorganisms involved in these processes. Aerobic microorganisms, which rely on oxygen to break down organic matter, become less active in cooler temperatures. This reduced activity can lead to decreased efficiency in the breakdown of solids, meaning that the solids remain in suspension for a longer period instead of settling out as sludge. When solids are not adequately broken down and settled, this can also lead to operational challenges in wastewater treatment, affecting the overall efficiency of the treatment process. In the context of the other options, a decrease in water temperature does not inherently improve gas exchange, nor does it generally lead to decreased oxygen levels in the water itself. Conversely, the settling efficiency of solids is impaired, not improved, as the activity of the microbial population decreases. Thus, the correct understanding aligns with how lower temperatures adversely impact the biological treatment processes critical for effective wastewater management.