Basic Wastewater Operator Practice Exam

In what situation would a clarifier likely overflow?

1. When the sludge blanket is too thick

2. When the flow rate is too low

3. During backwash cycles

4. When the influent is clear

The correct answer is: When the sludge blanket is too thick

A clarifier is designed to separate solid waste from liquid in wastewater treatment processes, and an overflow situation occurs when the volume of water surpasses the capacity of the clarifier. When the sludge blanket becomes too thick, it can cause several issues. As the sludge blanket thickens, it means there is a substantial accumulation of settled solids at the bottom of the clarifier. This accumulation can impede the subsequent settling process of incoming wastewater, leading to inefficient clarification. When the inflow of wastewater continues at a certain rate, the retention time within the clarifier decreases, which can lead to: 1. Poor settling of suspended solids – the thicker sludge blanket acts as a barrier, preventing proper settling of solids from the incoming water. 2. Increased hydraulic loading – with solids being less effective at settling or being released, there can be an overflow of clarified liquid, as the clarifier cannot adequately handle the volume of incoming wastewater. In contrast, low flow rates typically allow for better settling and clarification, while backwash cycles are designed to remove built-up solids without risking overflow if managed properly. Clear influent generally leads to better clarification, not overflow, since there are fewer solids to settle. Thus, a thick sludge blanket is the primary factor that can lead to