Sewage treatment

Sewage treatment removes physical, chemical, and biological contaminants from wastewater before its reuse or release into the environment.

Screening (water treatment): A preliminary treatment process that removes large debris from flowing wastewater with screens. Screens intercept rags, plastics, and other debris before they damage pumps or obstruct later stages.
Biochemical oxygen demand: A measure of the oxygen microorganisms consume while decomposing biodegradable organic matter in water. A drop in this measure indicates that biological treatment has removed biodegradable pollution.
Water reuse: The use of treated wastewater for a beneficial purpose instead of discharging it as waste. Treatment can produce water for irrigation, industry, or other uses when quality requirements are met.
Septic tank: An underground chamber that settles solids and begins anaerobic treatment of household wastewater. It treats wastewater on site rather than sending it through a centralized sewer and treatment plant.
Primary sedimentation: A settling process in which suspended solids sink from wastewater in a clarifier. Settling removes much of the material that can be separated without biological treatment.
Chemical oxygen demand: A measure of the oxygen equivalent needed to chemically oxidize substances in a water sample. It captures a broader range of oxidizable wastewater pollution than biochemical oxygen demand.
Effluent: Liquid discharged from a treatment process or industrial facility. Treated effluent is the outflow whose quality determines whether discharge or reuse is suitable.
Membrane bioreactor: A wastewater process combining biological treatment with membranes that separate solids from treated water. Its compact, high-quality effluent contrasts with conventional activated-sludge clarification.
Activated sludge: A wastewater treatment process in which aerated microbial flocs consume organic pollutants and are separated by settling. Its microbes remove dissolved and fine organic matter that primary settling leaves behind.
Total suspended solids: The concentration of solid particles suspended in a water sample. This measure tracks particles removed by screening, settling, and filtration.

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