Waste Water Treatment

Every day, homes, farms and factories produce vast quantities of waste water that must be treated before it can be safely returned to the environment. This lesson covers the stages of sewage treatment and the different sources and types of waste water, as required by the AQA GCSE Chemistry specification.

---

Sources of Waste Water

Waste water comes from several different sources, each containing different types of contaminants:

Source	Type of Waste Water	Main Contaminants
Domestic (homes)	Sewage	Human waste, detergents, food waste, microorganisms
Agricultural (farms)	Agricultural run-off	Fertilisers (nitrates, phosphates), pesticides, animal waste
Industrial (factories)	Industrial effluent	Heavy metals, organic chemicals, solvents, acids, alkalis

All of these must be treated before the water can be released into rivers, lakes or the sea. If untreated waste water enters waterways, it can:

• Cause eutrophication (excess nutrients lead to algal blooms that deplete oxygen)
• Spread waterborne diseases (cholera, typhoid, dysentery)
• Poison aquatic organisms with toxic chemicals or heavy metals
• Damage ecosystems and reduce biodiversity