Super Chlorination in Water Treatment Process| Well and Bore Hole Water
By ‘super chlorination‘ is meant the dosing of a water with a high dose of chlorine, often much larger than the usual condition of the water demands. The method is most often used on a borehole or well water which, though normally free of pollution, may be subject to the onset of pollution to an unknown degree following heavy rainfall or some other circumstances.
The normally unpolluted water may only require a small protective dose of chlorine of the order of 0.2 mg/1. To wait for the pollution to occur, detect it, and then increase the dose is impracticable since action could not take place in time to prevent some of the pollution passing into supply.
It is also used on heavily polluted river waters, where the pre-treatment process does not include a pre-disinfection stage. Therefore a continuous high dose and adequate contact time is given sufficient to counter the worst conditions likely. After the contact period the water can be partially de-chlorinated by the injection of sulphur dioxide or sodium bisulphite, and the dose may be so controlled that only a part is removed, leaving a residual to go into supply.
These processes of chlorination and partial dechlorination to achieve some given level of residual chlorine can be controlled automatically. Super chlorination can also sometimes be found helpful in the case of waters liable to give rise to taste and odours with lesser doses of chlorine.