Sewage treatment plants 

Sewage treatment, is the process of removing pollutants from municipal wastewater, which mainly contains domestic wastewater plus little industrial wastewater. Physical, chemical, and biological processes are used to remove pollutants and to produce treated wastewater (or treated effluent) that is safe enough to be released into the environment. The by-product of wastewater treatment is a semi-solid waste or slurry, called wastewater sludge.

Sludge must undergo further treatment before it is suitable for disposal or release into the ground. Sewage treatment can also be referred to as wastewater treatment. However, the latter is a broader term that can also refer to industrial wastewater. For most cities, the sewage system will also carry a proportion of the liquid industrial waste to the wastewater treatment plant, which usually receives pretreatment in the factories themselves to reduce the pollutant load.

If the sewage system is a communal sewage network, it will also carry running water from urban areas (rainwater) to the wastewater treatment plant. Wastewater can be transported to treatment plants via pipelines with liquefaction or with the use of pumps. The first part of wastewater purification usually includes a barrier to filter solids and bulky items, which are then collected in landfills and disposed of in landfills. Fat and grease are also removed prior to the initial wastewater treatment.