Which step is taken to prevent or control sludge bulking in the Activated Sludge Process?

In the Activated Sludge Process, chlorinating returned activated sludge serves as an effective method to prevent or control sludge bulking. Sludge bulking occurs when the floc-forming bacteria in the waste treatment system become less efficient, leading to the formation of a fluffy, poorly settling sludge that can disrupt the sedimentation process in clarifiers.

Chlorination can help in reducing the population of filamentous bacteria, which are often responsible for sludge bulking. By selectively targeting these organisms, chlorination encourages a healthier microbial balance that favors the growth of floc-forming bacteria, thus promoting better settling of the sludge. As a result, this method directly addresses the sludge bulking issue, enhancing the overall efficiency of the treatment process.

Other methods listed, such as adjusting aeration levels or altering the pH, may have indirect influences on sludge characteristics, but they do not specifically target the microbial imbalances responsible for bulking as effectively as chlorination does.