Tennessee Wastewater Operator Practice Exam

Why should RAS flow rates be kept low while meeting treatment goals?

1. To increase the SVI

2. To avoid sending excess water to solids handling

3. To reduce operational costs

4. To improve sludge settleability

The correct answer is: To avoid sending excess water to solids handling

Maintaining low Return Activated Sludge (RAS) flow rates while still meeting treatment goals is primarily aimed at avoiding the transmission of excess water to solids handling systems. When RAS flow rates are kept at appropriate levels, the balance between the quantity of sludge returned to the aeration basin and the sludge being wasted is optimized. This helps in retaining the necessary solids within the biological treatment system, ensuring that the biochemical processes are effective. High RAS flow rates can lead to a situation where too much water is redirected, causing a dilution of the solids and negatively affecting the overall efficiency of the treatment process. Sending excess flow to solids handling not only complicates solids management but can also result in issues such as increased costs due to the need for further treatment or disposal of additional solids. By keeping the RAS flow rates low, the treatment facility can effectively maintain the concentration of active microorganisms, which enhances treatment efficiency and reduces operational burdens related to handling excess solids. This approach is crucial for optimizing resource use and ensuring that the treatment system remains effective while minimizing excessive load on downstream processes.