Tennessee Wastewater Operator Practice Exam

When sludge settleability deteriorates, increasing RAS flow does what?

1. Improves blanket depth

2. Cleans the clarifier

3. Causes blankets to deepen

4. Reduces treatment efficiency

The correct answer is: Causes blankets to deepen

When sludge settleability deteriorates, increasing return activated sludge (RAS) flow generally causes the blankets to deepen. This occurs because the RAS carries with it a higher concentration of solids back into the aeration tank, which can become suspended in the clarifier. If the sludge is not settling properly due to deteriorated settleability, the additional RAS introduces more solids into the system, potentially leading to a deeper layer of sludge accumulation or sludge blanket in the clarifier. A deeper sludge blanket can hinder the settling process, exacerbating the situation of poor settleability and creating an environment where effluent quality could be compromised. Understanding this interaction is crucial for wastewater operators as it informs decisions on how to manage RAS flow rates to support optimum settling conditions in the clarifier. This phenomenon underscores the importance of proper sludge management and the maintenance of good operational practices to ensure effective wastewater treatment.