Wastewater treatment

Wastewater treatment removes physical, chemical, and biological contaminants from used water before it is discharged or reused. Treatment may also recover resources such as nutrients, energy, and water.

Screening (water treatment): A preliminary treatment step that removes large debris from wastewater using screens. Screens protect pumps and downstream equipment from rags, plastics, and other debris.
Biochemical oxygen demand: A measure of oxygen consumed by microorganisms as they decompose biodegradable material in water. It indicates the organic load that biological treatment must reduce.
Water reuse: The use of treated wastewater for beneficial purposes instead of discharging it as waste. Treatment can produce water for irrigation, industry, or other specified uses.
Eutrophication: The enrichment of water with nutrients that drives excessive plant or algal growth and ecosystem change. Insufficient nitrogen or phosphorus removal can contribute to eutrophication downstream.
Drinking water treatment: The treatment of source water to make it suitable for human consumption. It treats water before use, whereas wastewater treatment addresses water after use.
Primary treatment: The physical removal of settleable and floating solids from wastewater, usually by sedimentation and skimming. Settling tanks remove much of the suspended material before biological treatment.
Chemical oxygen demand: A measure of the oxygen equivalent needed to chemically oxidize substances in a water sample. It estimates total oxidizable pollution, including material resistant to biodegradation.
Water reclamation: The treatment of wastewater to produce water suitable for a defined beneficial use. Reclamation sets treatment targets according to the intended use.
Sludge treatment: Processes that stabilize, dewater, or otherwise prepare wastewater solids for disposal or beneficial use. Treatment concentrates pollutants into sludge that must be managed separately.
Membrane bioreactor: A wastewater process that combines biological treatment with membrane filtration to separate solids from effluent. It can replace conventional secondary clarification with a compact solids barrier.

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