Use of Chlorine in Swimming Pools
Chlorine, Iodine and Bromine can be used for disinfecting water but not fluorine because it is too reactive. Chlorine is often chosen simply because it is cheap, readily available and relatively easy to handle. Disinfection relies on disrupting a harmful organism’s metabolism or structure. That can be achieved by oxidation and non-oxidising chemicals which have similar effects, as well as by non-chemical processes such as ultraviolet (including sunlight), X-rays, ultrasound, heat (as in pasteurisation), variations in pH and even storage to allow organisms to die naturally. Chlorine gas consists of molecules of two chlorine atoms but no oxygen. When added to water, one of the atoms forms a chloride ion. The other reacts with water to form hypochlorous acid, an oxidising agent. Disinfection comes from the hypochlorous acid reacting with another molecule, most probably in the bacterial cell wall, in an oxidation-reduction reaction. If this happens enough times, the organism’s repair mechanisms are overwhelmed and it dies. So concentration of disinfectant and the length of time pathogens are exposed to it are important factors. Disinfection needs to be carried out under closely controlled pH conditions, ideally between 7 and 7.6. If the pH is too low — less than 6.8 — there is a tendency for nitrogen compounds, especially urea (a common pool contaminant) to degrade via another route to chloramines. The worst of these is nitrogen trichloride, which irritates the eyes and creates the so-called chlorine smell associated with poorly run or overused swimming pools.
Best time of Chlorination of Swimming Pool is Night Hours.
Chlorine, or more commonly a substance containing hypochlorite ion, is added to pools as a disinfectant. However, sunlight rapidly destroys hypochlorite, drastically reducing the effectiveness of the sanitizer. Hence, the effectiveness of the disinfectant is maximized when added in the evening hours.
Ozonation Versus Chlorination
Ozonation of water has strong virucidal effect. It inactivates viruses in a matter of seconds. Many countries around the world are using ozone for water treatment. Ozone has no residual germicidal effect, but in the case of chlorination there is residual effect over the germs. Combined treatment of water with ozone and chlorine effectively sterilise the water. 0.2 to 1.5 mg of ozone is necessary to sterilise one litre of water. As ozone destroys all micro organisms and it removes disagreeable odours, the resultant water is absolutely safe, pure, fresh and healthy. Ozonised water is colourless and odourless.