The Secondary Clariers receive the activated sludge from the Aeration Basins. Activated sludge consists of agglomerated sludge particles (called “floc”) and the microbes that are feeding on them. These floc particles readily join together to form larger floc particles that settle rapidly to the bottom of the clarifier. A special kind of bacteria called filamentous bacteria form networks between the floc particles. This network improves the clarity of the finished wastewater by acting as a filter during settling.
Most of the settled activated sludge is immediately returned to the aeration basins. That is how the microbe population is maintained. Of course, if something is being removed from the water, it has to go somewhere. Some of the settled activated sludge is removed from the system, a process reffered to as “wasting”. At this facilty, we transfer the waste sludge to the Primary Clarifiers, where it co-settles with the primary sludge and is pumped to the anaerobic digesters.
The clarified wastewater leaves the tank via the effluent weirs. As in the Primary Clarifiers, the purpose of the weirs is to provide a large withdrawal area that won't pull the settled sludge out of the tank. After the Secondary Clarifiers, treatment is essentially finished. In warm weather, the wastewater is chlorinated immediately after it leaves the clarifier. Effluent from the Secondary Clarifiers goes to the Chlorine Contact Tanks.