Any of the mechanical or chemical processes used to modify the quality of wastewater in order to make it more compatible or acceptable to humans - Source

Physical, chemical, and biological processes used to remove pollutants from wastewater before discharging it into a water body - Source

Chemical, biological, and mechanical procedures applied to an industrial or municipal discharge or to any other sources of contaminated water to remove, reduce, or neutralize contaminants - Source

What Is Water And Waste Water Treatment? Source

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Sewage Treatment, Or Domestic Wastewater Treatment:: Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater, both runoff (effluents) and domestic. It includes physical, chemical and biological processes to remove physical, chemical and biological contaminants. Its objective is to produce a waste stream (or treated effluent) and a solid waste or sludge suitable for discharge or reuse back into the environment. This material is often inadvertently contaminated with many toxic organic and inorganic compounds.