Important functions of chlorination:

Although the primary objective of chlorination of potable water is the destruction or inactivation of bacteria, there are several other important secondary functions achieved by chlorination. These include:

(a) The oxidation of iron, manganese and hydrogen sulphide.

(b) The destruction of some taste and odour producing compounds.

(c) Control of algae and slime organisms in treatment plants.

(d) As an aid to coagulation.

The requirements of effective chlorination are met when the chlorine dose is sufficient to meet excess or residual chlorine for disinfecting purposes in the water distribution system under the prevailing alkalinity and temperature of the water and also the contact time. In the developing countries like India a free chlorine residual of about 0.5 mg/l and combined residual chlorine of about 1.5 mg/l is recommended for clear water having a pH of about 7 and a contact time of about 30 minutes is generally used.