The process of treating wastewater to make it safe for disposal or reuse
Sources of wastewater
Domestic
Agricultural
Industrial
Domestic wastewater
Household waste like water from showers, sinks, and toilets
Agricultural wastewater
Nutrient runoff from fields and animal waste from farms
Industrial wastewater
Wastewater from factories that make and use chemicals
Sewage treatment
1. Screening
2. Sedimentation
3. Biological breakdown by microorganisms
Screening
Removing large objects like twigs or plastic bottles by passing the sewage through a mesh
Sedimentation
Allowing the sewage to sit in a tank so that the heavier solid bits sink to the bottom to form sludge, leaving a lighter effluent at the top
Biological breakdown
1. Aerobic digestion in the effluent tank
2. Anaerobic digestion in the sludge tank
Aerobic digestion
Breakdown of organic matter by microorganisms in the presence of oxygen
Anaerobic digestion
Breakdown of organic matter by microorganisms in the absence of oxygen
Sludge
The digested solid waste from the sedimentation process, which can be used as a fertilizer
Methane
A byproduct of anaerobic digestion that can be captured and burned as an energy source
Wastewater can contain toxic substances that require additional treatment steps to remove, such as adding chemicals to precipitate out metals or using UV radiation
Some countries with limited water supply, like Singapore, rely on treating wastewater for their drinking water supplies
