University of Tehran

Application of ozonation in drinking water disinfection based on an environmental management strategy approach using swot method

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Disinfection is the destruction of pathogenic microorganisms. It does not apply to nonpathogenic microorganisms or to pathogens that might be in the spore state (McCarthy and Smith, 1974). Chlorine is the most widely used disinfectant because it is effective at low concentration, is cheap and forms a residual if applied in sufficient dosage. It may be applied as a gas or as a hypochlorite, the gas form being more common. The disinfecting ability of chlorine is due to its powerful oxidizing properties, which oxidize those enzymes of microbial cells that are essential to the cells metabolic processes (Hammer et al., 2004). Dissolved chlorine will react with organic compounds, particularly unsaturated compounds. Two of the organo reactions are particularly important, those that result in chlorophenols and those that produce trihalomethanes. Chlorophenols formed from the reaction of chlorine with phenols, impart undesirable tastes and odors to water that are detectable at phenol concentrations less than one microgram per liter. Reaction of chlorine with innocuous humic substances results in the formation of trihalomethanes including  chloroform, bromoform, bromodichloromethane and dibromochloromethane. These compounds are limited by drinking water regulations to a total of 0.1 miligram per liter because of tumorigenic properties (White, 1998). Ozone is an allotrope of oxygen. It is a powerful oxidant and is more powerful than chlorine and other oxidants. In aqueous solution it is relatively unstable, having a half-life of 20 to 30 minutes at 20 degrees centigrade. The presence of oxidant-demanding materials in solution will render the half-life even shorter (Rice et al., 1979). Ozone is widely used in drinking water treatment practice in Europe. Its first application was in 1893 at Oudshoorn, Netherlands

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