Definition - It is the method of disinfection by which the micro organisms are killed in chlorine. Chlorination serves not only for disinfection, but as an oxidant for other substances (iron, manganese, cyanide, etc) and for taste and odor control in water and wastewater. Other chemical disinfectants include chlorine dioxide, ozone, bromine, iodine. The last two chemical are generally used for personal application & not for the public water supply.
TYPES OF CHLORINATION
1. Plain Chlorination Chlorination of water relatively free from suspended matter without any other
treatment.
2. Pre chlorination The application of chlorine to raw water before any other treatment to improve the coagulation and to remove the taste, odor & colour.
3. Post Chlorination Application of chlorine to treated water after all the other treatment. Dosage chlorine range from 0.25- 5.0mg/lit in order to obtain the combined residual chlorine in range of 0.1-0.2mg/lit.
4. Double chlorination Chlorine is added to raw water at more than one point. This is done when water is highly contaminated.
5. Break Point Chlorination It is the amount of chlorine that is, needed to destroy bacteria and to oxidise all the organic matter and ammonia cal substances present in the water. The point at which the chlorine demand of water sample is met is called the break point. If further chlorine is added beyond the break point, free chlorine in the form of HOCL (Hypochlorous acid) and OCI (Hypochlorite ion) begin to appear in the water.
6. Super chlorination This is done when there is epidemic in the area. The dose varies from 0.5 to 2.00 ppm depending upon the impurities of water.
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