California Wastewater Grade 3 Certification Practice Test 2025 - Free Wastewater Certification Practice Questions and Study Guide

Applying chlorine to the return activated sludge is a method that can effectively control filamentous organisms in wastewater treatment. Filamentous organisms often proliferate in activated sludge systems, leading to issues such as poor settling and anaerobic conditions, which can disrupt the treatment process. Chlorine acts as a strong disinfectant that can help reduce the population of these undesired filamentous organisms, allowing for better performance of the biological treatment process.

This action is particularly relevant in activated sludge systems, where filamentous bacteria can outcompete other microorganisms and create operational challenges. By using chlorine selectively on the return activated sludge, operators can reduce the filamentous biomass without harming the overall microbial community essential for effective wastewater treatment.

In contrast, decreasing flow to the system could lead to inadequate treatment and accumulation of solids. Letting nature manage the population might not provide the necessary control in a managed treatment environment, where specific actions are required to maintain performance. Increasing the Mean Cell Residence Time (MCRT) could actually favor filamentous organisms by allowing them more time to grow without being controlled, so while that option can affect overall biomass, it does not specifically target filamentous organisms effectively.