Secondary Treatment (Biological Process)

Activated Sludge

The primary treatment effluent flows to aeration basins where oxygen is added to encourage growth of useful bacteria and microorganisms naturally present in the wastewater. Microorganisms and bacteria consume organic material (food) in the wastewater aeration system/basin which goes to secondary clarifiers.

The clarifiers are large round sedimentation tanks where the microorganisms settle to the bottom of the tank. Some of the settled organisms are returned to the aeration basins to again be introduced to oxygen and a food source to become ‘activated’ to consume more organic material. The excess secondary sludge is pumped to the Solids Handling process to be thickened and sent for further processing in the anaerobic digesters. The water (effluent) from the secondary clarifiers (Final Settling) flows to the disinfection channel for disinfection.