# Describe the processes used in the treatment of sewage to produce water that is safe to release into rivers.

> Cambridge International IGCSE Chemistry (0620) — 10.1 Water · Describe · 4 marks

## Mark scheme (4 marks)

1. Screening / removal of large solid objects or debris
2. Sedimentation / settlement allows suspended solids to sink / form sludge
3. Biological / aerobic treatment where bacteria break down / digest organic matter
4. Chlorination / addition of chlorine to kill harmful microorganisms / bacteria before release

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