Wastewater Treatment Operator Certification Practice Test

What should be done if the SVI is high and there is an excess of normal filamentous microorganisms in the activated sludge process?

1. Inject hydrogen peroxide in the secondary effluent

2. Make sure DO levels are very low in the aeration tank

3. Decrease MLSS and sludge age

4. Chlorinate the return activated sludge

The correct answer is: Chlorinate the return activated sludge

In the scenario where the Sludge Volume Index (SVI) is high and there is an excess of filamentous microorganisms in the activated sludge process, chlorinating the return activated sludge helps control the excessive filamentous organisms. High filamentous growth often leads to poor settling characteristics, which is reflected in a high SVI. By applying chlorination to the return activated sludge, you can selectively inhibit or kill these filamentous bacteria while allowing the more desirable floc-forming bacteria to thrive. The process of chlorination is aimed at managing biological populations within the system effectively. Chlorine acts as a disinfectant that helps reduce filamentous growth, thereby improving the overall stability of the sludge and enhancing settling within the settling tanks. This contributes to better effluent quality and helps maintain an appropriate balance in the activated sludge process. While there are alternative methods to manage high SVI and excess filamentous organisms, chlorination directly addresses the root cause by targeting the problematic microorganisms, ultimately leading to improved operational efficiency in wastewater treatment processes.