Waste treatment refers to the activities required to ensure that waste has the least practicable impact on the environment. In many countries various forms of waste treatment are required by law.

The principal waste treatment processes are :

• Sewage treatment – treatment and disposal of human waste - Sewage is produced by all human communities and is treated using processes that separate solid materials by settlement and then convert soluble contaminants into biological sludge and into gases such as carbon dioxide or methane.
• Waste management – re-use, recycling and disposal of solid waste from manufacturing, commerce and domestic sources.
• Industrial wastewater treatment – the treatment of wet wastes from manufacturing industry and commerce including mining, quarrying and heavy industries
• Agricultural wastewater treatment – treatment and disposal of liquid animal waste, pesticide residues etc. from agriculture.
• Radioactive waste treatment – the treatment and containment of radioactive waste.