Wastewater, return activated sludge and pure oxygen are mixed in the aeration tanks. Each tank is actually a concrete box measuring 56 feet on all sides with a depth of 18 feet. The plant has four trains with 4 stages per train, a total of 16 tanks. Wastewater passes from the grit tanks to the oxygenation tanks, where large mixers dissolve oxygen into the sewage. The oxygen is required to maintain a suitable living environment for bacteria, which feed on organic matter in the sewage.
Natural processes convert pollutants to microorganisms.
The same process occurs in a natural waterway, only at a slower pace. Each tank is 160 feet in diameter. Here wastewater is detained to permit solids suspended in the water to flocculate and sink to the bottom, or float to the top. Large sweeping arms remove settled and floating materials from the tanks. Most sludge is returned to the aeration basins to be mixed with more wastewater and oxygen and to repeat the process.