At Delaware No. 1, pure oxygen is mixed with the wastewater in the aeration tanks. Activated sludge from the leveling ponds is mixed with the wastewater in the equalization tanks to begin biological digestion of organic contaminants. In the oxidation tanks, primary sludge settles to the bottom and can be removed. The wastewater is able to mix with air at this point. Activated sludge from the clarifiers is also mixed into the wastewater in the oxidation tanks.
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.