STERILIZATION OF WATER CAN BE DONE IN A NUMBER OF WAYS BUT CHLORINATION HAS BEEN FOUND TO BE THE MOST PRACTICAL, EFFECTIVE, CHEAPEST AND CONVENIENT METHOD FOR PUBLIC WATER SUPPLIES.

Chlorine is very active agent of and reacts quickly with organic matter present in the water. It is very effective against the bacteria commonly associated with water-borne diseases, and control of algae and other plant life. Chlorine eliminates tastes and odours, improves coagulation, oxidises iron and manganese and removes colour. Chlorine content in water 23 percent is supposed to be sufficient to kill all typhoid, cholera and gastroenteritis germs. But flue, colds and hepatitis germs are killed only by boiling water. Chlorine may be given in three forms (a) For very small supplies, as bleaching powder or chloride of lime. (b) For small town or village installations, as liquid or sodium or sodium hypochlorite solution containing 10 to 15 percent by weight of chlorine. The liquid form can be readily mixed with water. (c) For medium and large size water works, as chlorine gas by gaseous chlorinator. Chlorine is easiest to apply in the form of a solution. The chlorine may be added to the water in the pipe leading from the filtered water impounding reservoir to the distribution mains or in the clear well (made for the purpose) so that an adequate contact time will be ensured. Where the raw water is highly polluted it would be advantageous to add some chlorine into the suction pipes of raw water pumps or to the water as it enters the mixing chamber, before any other treatment is given. This pre- chlorination reduces the bacterial load, improves coagulation, reduces tastes, odours, algae and other organisms and keeps the filter sand cleaner, and also prevents decomposition of previously settled sludge. The dosage should be such that a residual of 0.1 to 0.5 ppm goes to the filters ;a dose of from 5 to 10 ppm is common . The requirements of chlorine depends upon the type of bacteria and the amount present in the water, and can be determined by orthotolodin test, however high degree of sterilization should not be done for public water supplies as it proves harmful in the long run :-- Er Fateh Chand Guleria, Director, RTI Welfare Association, Registered number HPCD 3552 Bilaspur Himachal Pradesh, Phone number 9459334377.

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