What is the purpose of a secondary clarifier in wastewater treatment?

The purpose of a secondary clarifier in wastewater treatment is fundamentally about separation. It is designed to allow the solid biomass, which includes microorganisms that have digested the organic matter in the wastewater, to settle out of the treated water. After the biological treatment phase, where microorganisms break down pollutants, the secondary clarifier plays a crucial role in ensuring that the clarified water can be separated from these solids before further treatment or discharge.

The process involves gravity settling, where the heavier biomass settles to the bottom of the clarifier, forming a sludge blanket, while the clearer effluent is collected from the top. This step is essential because it helps achieve a clear effluent by reducing the volume of suspended solids and allows for the recycle or disposal of the settled biomass. Therefore, the secondary clarifier is integral to producing treated water that meets regulatory standards and is safe for either discharge into the environment or for further treatment processes.