Tennessee Wastewater Operator Practice Exam

How can the biological activity in an activated sludge plant be compensated during cold weather?

1. Increase the MLSS beyond normal levels

2. Decrease the aeration time

3. Lower the temperature of the incoming wastewater

4. Add supplementary nutrients

The correct answer is: Increase the MLSS beyond normal levels

In an activated sludge plant, the biological activity is highly dependent on temperature, with colder temperatures generally leading to reduced microbial activity and slower reaction rates in the treatment process. One effective method to compensate for diminished biological activity during cold weather is to increase the mixed liquor suspended solids (MLSS) beyond normal levels. Increasing MLSS allows for a higher concentration of microorganisms in the system. Even when the temperature drops, having more microbial mass can help maintain the necessary biological processes for effective treatment. With a greater population of microbes present, the overall biological activity can be sustained, enabling the plant to continue effectively removing pollutants even in unfavourable temperature conditions. Other methods, such as modifying aeration time or adding nutrients, may also support the process but do not directly address the need for increased microbial presence within the system to offset the effects of low temperatures. Moreover, reducing the temperature of the incoming wastewater is not a feasible option, as it would further decrease the overall reaction rates in the treatment system.