Water flowing off the top of the Aeration basin flows into the Secondary Clarifier. Here the water slows again, so that heavier particles settle to the bottom. Light particles such as foam or scum float on the surface and are skimmed off the top and sent to the Digester. Pumps draw the heavy sludge off the bottom of the Clarifier. 50% to 90% is returned to the Aeration Basin to reseed the bacteria in the basin and allowing the bacteria to remove more organic materials. The remaining sludge is sent to the Digester. The clean water from the Clarifier is then directed to the Equization Pond.
At times to help with nutrient removal, the sludge is redirected to a Re-aeration Basin before being sent back to the Aeration Basin. This is done so that the air can be cycled on and off to improve the process.