What is the primary function of a secondary clarifier in wastewater treatment?

The primary function of a secondary clarifier in wastewater treatment is to separate and thicken sludge. In the secondary treatment process, biological treatment occurs where microorganisms break down organic matter in the wastewater. After this biological treatment, the mixed liquor, which consists of treated wastewater and biomass, flows into the secondary clarifier.

In the clarifier, the denser biomass settles to the bottom, forming a thickened sludge layer, while the clarified water is collected from the surface and sent for further treatment or discharge. This separation is crucial because it ensures that the biomass is effectively removed from the treated effluent, allowing for clearer water output and the possibility of returning a portion of the settled sludge back to the biological treatment process to maintain adequate microbial populations.

While the other options refer to important aspects of wastewater treatment, they do not accurately represent the main role of the secondary clarifier. Aeration is typically handled in aeration tanks, the removal of dissolved pollutants occurs primarily through chemical processes or advanced treatment techniques, and disinfection is usually done in a separate step after secondary clarification.