Q.Give an account of control of water pollution.

Water pollution is controlled by treating sewage and industrial effluents before discharge, reducing the input of fertilizers/pesticides and other pollutants, using biological treatment methods, and enforcing pollution-control legislation.

Note: this topic corresponds to the pre-rationalisation NCERT 'Environmental Issues' chapter, which is not part of the current rationalised chapter set provided; it is answered here from general environmental-science knowledge for completeness.

1. Sewage and wastewater treatment: Domestic sewage and industrial effluents are the largest sources of water pollution (organic load, pathogens, heavy metals, toxic chemicals). Treatment before release into water bodies typically involves:

• Primary treatment - physical removal of large solids by screening, grit removal and sedimentation.
• Secondary (biological) treatment - aerobic microorganisms (activated sludge process) break down dissolved and suspended organic matter, reducing the Biochemical Oxygen Demand (BOD).
• Tertiary treatment - removal of remaining nutrients (nitrates, phosphates), pathogens (disinfection, e.g. chlorination/UV) and dissolved solids before safe discharge or reuse.

2. Reducing agricultural run-off: Excess use of chemical fertilizers and pesticides washes into rivers and lakes causing eutrophication and toxic contamination; controlled/judicious use, use of biofertilizers and integrated pest management reduce this input.

3. Biological/constructed methods: Constructed wetlands and controlled use of aquatic plants (e.g., water hyacinth in a managed setting, or reed beds) can absorb excess nutrients and some pollutants (phytoremediation) before water is released downstream.

4. Control of industrial and other point-source pollution: Industries are required to treat effluents to prescribed standards (Effluent Treatment Plants, ETPs) before discharge; solid waste and hazardous/radioactive waste must be properly contained and not dumped into water bodies.

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