Waste Water Treatment
Waste water is any water that has been used and contaminated, including sewage, agricultural run-off, and industrial waste. It must be treated before being released back into the environment.
Why treat waste water?
- It contains harmful microbes, organic matter, and toxic chemicals
- Untreated waste water can cause pollution, disease, and damage ecosystems
💡 Water treatment ensures waste water is safe for release or reuse.
Sources of waste water
Source | Examples |
Domestic | Sewage from toilets, sinks, showers |
Agricultural | Fertiliser run-off, animal waste |
Industrial | Factory chemicals, metal waste |
Stages of waste water treatment
- Screening – removes large solids (e.g. twigs, nappies)
- Sedimentation – heavier solids settle to form sludge, leaving effluent
- Aerobic digestion – bacteria break down organic matter in the effluent
- Anaerobic digestion (sludge only) – bacteria break down sludge without oxygen, producing biogas
- Sterilisation – may be used to kill harmful microbes
Comparing treatments
Type of Water | Treatment Required |
Fresh water | Filtration and sterilisation |
Seawater | Desalination (expensive) |
Waste water | Multiple steps (screening, digestion, etc.) |
Uses of treated waste water
- Released into rivers or seas
- Can be reused for irrigation, industrial processes, or even drinking (with extra treatment)
Questions
- What are the first two stages of waste water treatment?
- What is the name of the solid that settles at the bottom during sedimentation?
- What type of bacteria breaks down sludge?
- What gas is produced during anaerobic digestion?
- Which type of water treatment uses the most energy?
Summary
- Waste water comes from homes, farms, and factories
- Treatment involves screening, sedimentation, and biological digestion
- Sludge is broken down anaerobically to produce biogas
- Effluent is cleaned aerobically and returned safely to the environment
- Waste water treatment is more complex than fresh water treatment but uses less energy than desalination