Wastewater Treatment Operator Certification Practice Test

What is the typical detention time for a primary clarifier?

1. 3 to 4 hours

2. 30 minutes

3. 6 hours

4. 1.5 to 2 hours

The correct answer is: 1.5 to 2 hours

The typical detention time for a primary clarifier is usually within the range of 1.5 to 2 hours. This timeframe is crucial for allowing sufficient time for the solids in the wastewater to settle out, which is the primary function of the clarifier. During this process, heavier particles settle to the bottom, forming sludge, while lighter particles and scum float to the surface. Having a detention time of 1.5 to 2 hours optimizes the separation process, ensuring that the clarifier operates efficiently. A shorter detention time might not allow enough time for effective settling, leading to higher turbidity in the effluent. Conversely, excessively longer detention times could result in inefficient use of space and resources. Balancing these factors ensures that the primary clarifier meets its objectives in the wastewater treatment process effectively.