If your system was installed as a replacement to a septic system, your original septic tank may have been used as a trash tank. This will extend the time between pumpings and the life of your components.
The first compartment/tank an aerobic treatment unit (ATU) is the pre-treatment tank. In this tank the solids separate and sink to the bottom, while the fats, oils, and greases float to the top. This compartment contains anaerobic bacteria that break down the wastewater solids about 33% and produce the familiar foul odor of sewage. This tank acts similar to the traditional septic system. From this compartment the liquid waste flows into the secondary treatment process known as the aeration compartment.
An aerobic treatment unit or ATU is an extended aeration activated sludge process. This type of treatment depends primarily upon the use of air that is introduced to the wastewater from the solids compartment. When air is introduced it promotes the growth of aerobic organisms that breakdown the organic solids in the wastewater by about 66% producing inorganic and stable organic solids. The use of air is called aeration and this aeration provides dissolved oxygen, mixing of the wastewater and enough time for the organisms or bacteria to breakdown the organic solids that have entered the wastewater treatment plant. In the aeration chamber the wastewater is milk chocolate in color. As the wastewater leaves the aeration chamber it enters a quiet zone where no mixing occurs. The quiet zone is referred to as a clarifier.
In the clarifier the solids separate from the liquid again and settle to the bottom of the clarifier, that matter is called sludge. This sludge contains dissolved oxygen and this oxygen activates the bacteria it contains. This activated sludge is returned to the aeration chamber to be re-mixed. The sludge mixes with the incoming wastewater and this mixture of sludge and wastewater is referred to as mixing liquor. This mixed liquor flows back into the clarifier, the solids separate and return again to the aeration chamber.
The water that separates from the solids in the clarifier flows out of the wastewater treatment plant into the pump compartment and is referred to as effluent. The effluent is then chlorinated and sent to discharge. The chlorinated water, which should be around 99% clean, is then discharged through the sprinklers.