Tennessee Wastewater Operator Practice Exam

How does increasing recirculation rates affect the D.O. content of trickling filter effluent?

1. It decreases it

2. It has no effect

3. It stabilizes it

4. It would increase it

The correct answer is: It would increase it

Increasing recirculation rates in a trickling filter system leads to an increase in the dissolved oxygen (D.O.) content of the effluent. This is primarily because enhanced recirculation facilitates better mixing and contact between the water and the air. As the water is recirculated, it accumulates more oxygen from the atmosphere, which is critical in aerobic processes such as biological treatment in trickling filters. When wastewater is recirculated through the filter media, the additional oxygen created during this process supports the growth of aerobic microorganisms that are pivotal in breaking down organic matter. This microbial activity not only contributes to the treatment process but also helps to maintain higher levels of D.O. in the treated effluent. Furthermore, higher recirculation rates can improve the overall efficiency of the trickling filter by ensuring more uniform distribution of flow over the media, thus enhancing the treatment capabilities. Therefore, as the recirculation rates increase, the D.O. concentration in the effluent is positively impacted, supporting more effective biological treatment.