Tennessee Wastewater Operator Practice Exam

If the SVI increased from 120 to 210, what action should the operator consider?

1. Increase the SLR

2. Reduce the SLR

3. Increase RAS flow

4. Use chemicals for sludge treatment

The correct answer is: Reduce the SLR

An increase in the Sludge Volume Index (SVI) from 120 to 210 indicates that the mixed liquor in the system has become less dense and is settling poorly. SVI reflects the volume occupied by a given weight of sludge and helps assess the settling characteristics of activated sludge. A higher SVI generally suggests that the sludge is fluffier or less compact, which can lead to issues like poor settling, rising sludge in clarifiers, or increased quantities of sludge in the system. Reducing the Solids Load Rate (SLR) is a prudent action in this scenario because it lowers the amount of solids being fed into the treatment process. By decreasing the SLR, the operator can decrease the concentration of solids that the microorganisms need to manage. This reduction helps to balance the biological activity and sedimentation process, allowing the settling characteristics to improve. In turn, this may help reduce the SVI to a more acceptable level, ensuring efficient operation and addressing any potential issues arising from poor sludge settlement. Other options, such as increasing the SLR, increasing the return activated sludge (RAS) flow, or using chemicals for sludge treatment, might exacerbate the settling problem rather than resolve it. Increasing the SLR could add more solids to the system,