Tennessee Wastewater Operator Practice Exam

What happens to the MLSS concentration as the SRT increases?

1. It increases

2. It decreases

3. It is not affected

4. It stabilizes

The correct answer is: It increases

As the solids retention time (SRT) increases, the mixed liquor suspended solids (MLSS) concentration typically increases as well. This is because a longer SRT allows for more time for microorganisms to proliferate and form new biomass, which contributes to the overall MLSS in the system. Additionally, when the SRT is prolonged, there is less washout of the microorganisms from the system, leading to a higher accumulation of solids. This is particularly important in biological wastewater treatment processes, where the control of SRT is essential to maintain the right balance of active biomass for effectively breaking down organic matter. Overall, a longer SRT enhances the establishment of a stable population of microorganisms, thus increasing the concentration of MLSS in the treatment system. This can also positively influence the treatment efficiency, as a higher concentration of biomass can improve the capability of the system to handle organic loads.