Tennessee Wastewater Operator Practice Exam

An operator notices billowing clouds of sludge at the edges of the secondary clarifiers. What is the most likely cause?

1. Hydraulic surge

2. Excessive ventilation

3. Poor chemical dosing

4. Equipment malfunction

The correct answer is: Hydraulic surge

The presence of billowing clouds of sludge at the edges of the secondary clarifiers is most commonly associated with hydraulic surge. This phenomenon occurs when there are sudden changes in flow rates or volume entering the clarifier, which can cause turbulence and disrupt the settling process of the sludge. When hydraulic surges happen, the increased flow can lead to turbulence that resuspends settled solids, creating the observable clouds of sludge. In normal operations, secondary clarifiers are designed to allow for the settling of treated wastewater, where sludge is meant to fall to the bottom. However, if there is a sudden influx of water, perhaps from inflow from storm events or upstream process fluctuations, that can lead to disturbances, prompting the sludge to rise again. Understanding the flow dynamics and the potential for hydraulic surge is essential for operators to minimize disruptions and maintain optimal clarifier performance. The other options, such as excessive ventilation, poor chemical dosing, and equipment malfunction, could also affect clarifier performance but they typically would manifest in different ways and are less closely related to the specific visual indication of sludge billowing. For example, excessive ventilation might lead to aeration issues but generally wouldn’t cause the same visible disturbance in the clarifier itself.