Wastewater New York State Practice Exam

What would be considered a typical design detention time for a primary clarifier?

1. 0.5 hours

2. 1.5 hours

3. 3 hours

4. 6 hours

The correct answer is: 1.5 hours

The typical design detention time for a primary clarifier is generally around 1.5 hours. This duration is essential for allowing sufficient settling of solids from the wastewater being treated. During this time, heavier particles gravitate to the bottom to form sludge, while lighter materials, such as fats and greases, may float to the surface, forming scum. This efficient separation process is crucial for preparing the wastewater for further treatment stages. Designing for an appropriate detention time helps to optimize the removal of suspended solids and other particulates, directly influencing the overall effectiveness of the wastewater treatment process. If the detention time is too short, solids may not settle adequately, leading to increased turbidity and poor water quality. Conversely, excessively long detention times can lead to operational inefficiencies and increased costs. Thus, 1.5 hours strikes a balance that aligns with typical design specifications and operational goals in primary clarification.