Chlorination of Water

the treatment of water with chlorine and its compounds. The most widespread means of water disinfection, chlorination is based on the ability of free chlorine and its compounds to inhibit the enzyme systems of microorganisms that catalyze oxidation-reduction processes. Chlorine, chlorine dioxide, chloramines, and chlorinated lime are used to disinfect drinking water. The amount to be added is established by sample water chlorination: it is determined by the chlorine absorptivity of the water, that is, the amount needed to combine with the organic compounds that predominate in the water. An excess amount of chlorine (residual chlorine) is introduced in order to destroy microorganisms that find their way into the water after chlorination. The content of residual free chlorine 30 minutes after chlorination should be no less than 0.3 mg/liter. In some cases, water is chlorinated twice, before purification (preliminary chlorination) and after purification (final chlorination). Should substances exist in water that may give it an unpleasant odor or aftertaste after chlorination, the water is treated with ammonia or ammonium salts before chlorination.

Chlorination is used to disinfect drinking water under field conditions; the most reliable method in this case is superchlorination, which provides an excess of active chlorine no less than 10 mg/liter upon exposure of at least 30 minutes. Superchlorination is also used to disinfect water in centralized water-supply systems when there are epidemiological indications. Superchlorination is followed by dechlorination, that is, the removal of excess chlorine by physical or chemical methods.

Chlorination is also used to disinfect waste waters and the water in swimming pools, to bleach various materials, and to remove iron from industrial wastes.