Environmental Science (2+1)

Prevention and control of water pollution

• Natural purification of chemically contaminated groundwater can take decades and perhaps centuries, and cleanup efforts are sometimes much too expensive to be practical. The best way, then, to control groundwater pollution is to prevent it from occurring in the first place. Laws related to solid and hazardous waste disposal now significantly reduce new contamination. Not only are physical barriers between the waste and the groundwater required, but monitoring wells must be installed in some cases to provide early warning of possible leakage.


• Land-use management applied on the local level by towns and cities can be effective in preventing aquifer contamination. For example, zoning ordinances that prevent residential or industrial development in areas that are known groundwater recharge zones can reduce pollution problems. Strict enforcement of regulations pertaining to the siting, design, and construction of septic systems can reduce or eliminate the incidence of sewage contamination of private wells. Prudent application of pesticides and fertilizers in agricultural areas can also be effective in this regard.


• Control of water bodies and of organism serving the purpose of water protection should be reinforced and carried out by all available means including legal enforcement under the provisions laid down in water (prevention and control of pollution) Act 1974 and Environmental (protection) Act, 1986. The various ways / techniques suggested for prevention and control of water pollution are as follows.

1. Stabilization of Ecosystem

• This is the most reliable way to control water pollution. This would involve reduction in waste input, trapping of nutrients, fish management and aeration. Some of species of algae such as chlorella spirulina are excellent biological oxidants that can be used to reduce pollution load in a water body. Water hyacinth, Eichhornia crassipes , a luxuriantly growing weed may also be employed to remove phosphorus, nitrogen from a water body. It can also reduce BOD, COD and organic carbon.

2. Reutilization and recycling of waste

• Various kinds of wastes such as paper pulp, municipal and industrial effluents, sewage and thermal pollutants can be recycled to advantage. For example, urban waste could be recycled to generate cheaper fuel gas and electricity.

3. Removal of pollutants

• The various physico-chemical devised for removal of chemical, biological or radiobiological pollutants involve adsorption, electrodialysis, ion exchange and reverse osmosis. Of the various techniques, reverse osmosis deserves special mention. This technique is based on the removal of salts and other substances from water by forcing the later through a semi permeable membrane under a pressure that exceeds the osmotic pressure so that flow is in the reverse direction to the normal osmotic flow. Techniques devised by CSIR for the control of water pollution have been successfully employed for the removal and reuse of pollutants from industrial effluents.
1. Removal of ammonia from industrial waste water: Ammonia is removed in the form of ammonium sulphate which can be reused for the manufacture of fertilizer.
2. Removal of mercury: Mercury thrown out from chlor-alkali plants is removed and recovered by mercury –selective ion exchange resin.
3. Removal of phenolics: Phenolics in waste water from pulp, paper mill, petroleum refineries, tanneries etc are removed by the use of polymeric adsorbents.
4. Decolorization of water: An electrolyte decomposition technique has been developed to decolorize the sample of saree dying and printing industries.
5. Removal of sodium salts: Reverse osmosis technique has been developed to recover sodium sulphate from rayon mill effluent.