Conventional septic system overview
The simplest of all systems, this design has no moving parts other than gravity fed water and solids migrating through the system. Waste from the home is feed into the first septic tank where treatment begins. Tank treatment occurs in 3 ways, Settlement, Flotation and Bacterial Ingestion. The design of the tank allows only the clearest (effluent) layer of the waste water to migrate to the following tank. The second tank mostly relived of accumulated solids can further clarify the waste water before flowing to the final stage of ground treatment occurring in the drain fields.
More on conventional septic systems
In the pre-treatment portion of a septic system, many of the contaminants are removed from the wastewater in order to prepare it for final treatment and discharging into the environment. Contaminants in the wastewater include harmful bacteria that can cause illness, as well as nitrogen and phosphorus that can stimulate algae growth in water bodies.
The main unit of the pre-treatment portion of the system is a tank – commonly called a septic tank. Septic tanks are used to settle out solids and partially treat wastewater before it reaches the distribution system. Septic tanks should be made of reinforced concrete, polyethylene or prefabricated fiberglass. Many of the septic tanks used now are two-compartment tanks, as seen in this illustration.
Multiple tanks can improve sludge and scum removal. Sludge are the solids that fall to the bottom of the tanks (in a two compartment tank, most falls to the bottom of the first tank), and scum is the fats, oils and grease that float on the top of the water in the tank.