Important methods employed for disinfection are chlorination,ultra violet system and ozonation.
Chlorination is the most widely used disinfection method. Effectiveness of chlorine depends on factors such as pH,temperature,contact time and residual free chlorine. Chlorine is available in different forms. Calcium hypo chlorite usually in powder form with 65% chlorine by weight. Sodium hypo chlorite is available in the liquid form with 10-15% strength. Chlorine gas available in cylinders with 99.5% pure, used generally for large water systems.
Ultraviolet energy causes permanent deactivation of micro-organisms by disrupting DNA so that they are no longer able to maintain metabolism or reproduction. The maximum effectiveness occurs between 240 - 280 nm with the most effective wavelength typically at 254 nm. All bacteria, spores,viruses and protozoa are permanently deactivated by UV. UV dose is the most critical success factor for UV disinfection equipment. UV dose and reliability across flow rates is one of the most important features of a UV system.
Ozone is a triatomic allotrope of oxygen. It is a colourless gas with pungent odour. Ozone is 3000 times more powerful disinfectant than chlorine. Ozone is generated by an electrical discharge through dry air. Ozone when dissolves in water kills all micro-organisms,oxidises the organics and breaks them into more biodegradable compounds.