Basic Wastewater Operator Practice Exam

What should be done if the clarifier shows signs of fallback sludge?

1. Increase the flow rate

2. Flush the clarifier

3. Reduce return sludge rates

4. Adjust polymer dosage

The correct answer is: Reduce return sludge rates

When a clarifier shows signs of fallback sludge, it typically indicates a problem with the settling characteristics of the sludge being removed from the clarifier. One of the primary actions that can be taken in response to this situation is to reduce the return sludge rates. Reducing the return sludge rate helps to decrease the amount of settled solids being sent back into the clarifier, which can alleviate the excessive buildup of sludge within the system. By doing this, the clarifier can create better conditions for settling and more effectively separate solids from the clarified water. This adjustment helps ensure that the solids that are supposed to be removed effectively settle at the bottom of the clarifier instead of being resuspended and falling back into the flow. In contrast, other options, like increasing the flow rate, flushing the clarifier, or adjusting polymer dosage, may not effectively address the immediate issue of fallback sludge. Increasing flow might exacerbate the problem, causing even more solids to be swept into the effluent. Flushing the clarifier may temporarily clear some solids but will not resolve the root cause if it is related to sludge return rates or settling processes. Adjusting polymer dosage can be beneficial for improving coagulation and settling but is not a direct action that tackles the observation of fallback