Onsite sewage facility

Onsite sewage facilities (OSSF), also called septic systems, are wastewater systems designed to treat and dispose of effluent on the same property that produces the wastewater, in areas not served by public sewage infrastructure. A septic tank and drainfield combination is a fairly common type of on-site sewage facility in the Western world. OSSFs account for approximately 25% of all domestic wastewater treatment in the US. Onsite sewage facilities may also be based on small-scale aerobic and biofilter units, membrane bioreactors or sequencing batch reactors. These can be thought of as scaled down versions of municipal sewage treatment plants, and are also known as "package plants." The primary mechanism of biological waste recycling in the natural environment is performed by other organisms such as animals, insects, soil microorganisms, plants, and fungi, which consume all available nutrients in the waste, leaving behind fully decomposed solids that become part of topsoil, and pure drinking water that has been stripped of everything that can possibly be consumed and utilized. This natural biological purification requires time and space to process wastes. In virtually all engineered onsite sewage facilities, recycling and decomposition by natural organisms is still the primary mechanism of sewage disposal. Giving the organisms the time they need to decompose wastes is accomplished by establishing minimum sewage retention and settling times, and minimum liquid flow distances between sewage disposal sites and surface water or water wells. It is normal for animals such as mice, rats, flies, and parasites to participate in the fully natural biological waste recycling process. Engineered facilities typically attempt to exclude them to prevent out of control population explosions and infestation, and prevent spread of vermin and disease.