Bacteria grow in the oxidation tanks to consume organic material in the wastewater. The ambient air process used at Winslow requires mixing air into the wastewater repeatedly to allow enough exposure to oxygen. Unlike the process at Delaware No. 1, where the aeration tanks are enclosed in a building and kept at an elevated temperature, the Winslow plant uses an open air process at ambient temperature. If needed, the wastewater passes through the second stage aeration tanks for additional bacterial processing. Activated sludge is removed from the bottom of the clarifiers and either returned to the oxidation ditches or sent to the digesters for further processing.
More sludge settles out in the leveling ponds.
Sludge removed from the leveling ponds is returned to the equalization tank, at the beginning of the process. Backwash from the filters is held in the backwash decant tank, then returned to the equalization tank to be processed through the system again. The final stage of treatment takes place in the chlorine contact tanks. To kill any remaining bacteria, the water is mixed with a solution of sodium hypochlorite. It takes about 24 hours for water to pass through the Winslow plant.