Tennessee Wastewater Operator Practice Exam

What is the main purpose of the secondary clarifier in an activated sludge process?

1. Filtration of impurities

2. Separation of solids from liquids

3. Temperature control

4. Mixing of wastewater

The correct answer is: Separation of solids from liquids

The main purpose of the secondary clarifier in an activated sludge process is the separation of solids from liquids. After the biological treatment stage in the activated sludge process, where microorganisms break down organic matter, the mixture of treated wastewater and suspended solids (or biomass) flows into the secondary clarifier. In this step, the goal is to allow the heavier solids, primarily comprising the activated sludge floc, to settle at the bottom of the clarifier. This sedimentation process effectively removes the majority of the solids from the liquid phase, allowing for the clear effluent to exit the clarifier. The settled solids can then either be returned to the aeration tank to maintain the microbial population for further treatment or removed as waste sludge. While filtration of impurities, temperature control, and mixing of wastewater each play roles in various processes, they are not the primary functions of the secondary clarifier in the context of an activated sludge system. The focus here is specifically on the efficient separation and settling of solids, which is crucial for ensuring that the liquid effluent meets treatment standards before being discharged or further processed.