Principles of Chlorination

Principles of Chlorination

Principles of chlorination The mere addition of chlorine to water is not chlorination. There are certain rules which should be obeyed in order to ensure proper chlorination:

1. The water to be chlorinated should be clear and free from turbidity. Turbidity impedes efficient chlorination.

2. The chlorine demand of the water should be estimated. The chlorine demand of water is the difference between the amount of chlorine added to the water, and the amount of residual chlorine remaining at the end of a specific period of contact (usually 60 min), at a given temperature and pH of the water.

In other words, it is the amount of chlorine that is needed to destroy bacteria, and to oxidise all the organic matter and ammoniacal substances present in the water. The point at which the chlorine demand of the water is met is called the "break point". If further chlorine is added beyond the break point, free chlorine (HOCI and OCI) begin to appear in the water.

3. The presence of free residual chlorine for a contact period of at least one hour is essential to kill bacteria and viruses. It should be noted however, that chlorine has no effect on spores, protozoan cysts and helminthic ova, except in higher doses.

4. The minimum recommended concentration of free chlorine is 0.5 mg/l for one hour. The free residual chlorine provides a margin of safety against subsequent microbial contamination, such as may occur during storage and distribution. The sum of the chlorine demand of the specific water plus the free residual chlorine of 0.5 mg/l constitutes the correct dose of chlorine to be applied.

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