More than 1.5 billion people in developing nations are still without safe drinking water. Waterborne diseases such as typhoid, cholera, dysentery, amebiasis, salmonellosis, shigellosis, and hepatitis claim many innocent live each year.
Current drinking water disinfection practices provide the means to control most pathogenic bacteria, viruses, helminths, and protozoa responsible for the major waterborne diseases. However, some outbreaks still occur in these countries owing to continuing problems involving consumption of untreated water, errors of insufficient or interrupted disinfection, failures to maintain adequate levels of residual disinfectant in potable water distribution systems, and/or breaches in the systems.
Beside disinfection, drinking water treatment practices cover the entire spectrum of the various kinds of water treatment that are out there. This include coagulation, flocculation, settling, and filtration to remove suspended particles; stripping and chemical oxidation to reduce objectionable taste, odour, or colour; and precipitation, softening, pH control, or other operations designed to produce safe and aesthetically acceptable finished water from a raw water source, reliably and cost effectively.
Chlorination has been the predominant method of drinking water disinfection for more than 70 years. Chlorine, a strong oxidizing and disinfecting agent, is an effective micro biocide against most waterborne pathogens. It is inexpensive and relatively convenient to produce, store, transport, and use. Its high solubility in water makes it easy to dose in controlled amounts either as chlorine gas, which readily dissolves in water at room temperature, or as a salt of hypochlorite, which is formed by the reaction of chlorine and water as follows:
Cl2 + H2O = HOCl + H+ + Cl–
HOCl + H2O = H+ + OCl–
During chlorination, the relative concentrations of the hypochlorous acid (HOCl) and hypochlorite ions (OCl–), together termed ”free chlorine,” are determined mainly by measurement of pH. HOCl, a more effective biocide than OCl–, dissociates into OCl– between a pH of 7.0 and 8.0, the range in which most potable water undergoes treatment.
Traditionally, chlorine has been used in its gas form and dosed in water. Nonetheless, because it is a gas at room temperature it can present safety problems, especially during transportation and storage. Hence electro chlorination has emerged as a method of choice for chlorination as it is safer, uses no chemicals (just salt , water and electricity), easier to maintain and less expensive in the long run.