Tennessee Wastewater Operator Practice Exam

For which of the following trickling filter problems would you not increase the recirculation rate?

1. Icing

2. Clogging

3. Excessive Bacteria Growth

4. Odor Issues

The correct answer is: Icing

Increasing the recirculation rate in a trickling filter system is generally used to enhance the biological treatment process by returning a portion of the treated effluent back to the filter, promoting better distribution and more contact between the wastewater and microbial populations. However, for certain issues, this practice may not be beneficial or appropriate. Icing is an issue that arises during cold weather, where the surfaces of the trickling filter can freeze, impeding the operation and causing mechanical problems. In this situation, increasing the recirculation rate could exacerbate the problem by introducing more effluent, which could freeze more readily. Instead, addressing icing typically involves maintaining warmer conditions or reducing the flow to avoid the creation of additional ice, rather than increasing recirculation. In contrast, problems like clogging, excessive bacteria growth, or odor issues typically benefit from increased recirculation. For example, recirculation can help to break up clogs and distribute biomass more evenly, or it can dilute excessive concentrations of bacteria and help manage odors by promoting better aerobic conditions. Understanding how to respond to specific challenges in trickling filter systems is crucial for effective wastewater treatment operation.