Before discharging the foul sewage into rivers it is generally treated by

Before discharging into rivers, sewage undergoes multi-stage treatment including preliminary screening, primary sedimentation (settling solids), secondary biological treatment (aerobic bacteria to break down organics), and often tertiary disinfection (UV, chlorine) to remove pathogens, using processes like screening, sedimentation, aeration (oxidation), sludge digestion, and disinfection to make it safe.