The most important source of environmental pollution in underground waters, rivers, lakes and seas is wastewater. In addition to polluting water resources, wastewater also causes food pollution by being included in the food chain. Waste water should be collected from settlements and removed and make harmless. For this purpose, to be able to restore some or all of the chemical, physical and bacteriological properties of water lost by turning into wastewater as a result of various uses and/or in order not to change the physical, chemical and bacteriological properties of the environment in which they are discharged, one or more of the physical, chemical and biological treatment processes are applied together.

The sewage system that collects domestic and/or industrial waste water and the systems and facilities where the waste water is purified and the purified waste water is delivered to the receiving environment are called waste water infrastructure facilities. The system consisting of interconnected pipes or channels, which are used to collect, remove and transmit domestic or industrial wastewater and rain water to purification plants, is called a sewage system. From the moment it is formed, the waste water passes through different structures of the sewage system until it reaches the purification plant. First, the wastewater passes through the wastewater system of the buildings. Afterwards, it comes to the purification plant by passing through the manhole, connection channel, sewer pipes, chimneys, pumping stations, respectively.