Effectiveness of iodine for the disinfection of swimming pool water.

Abstract

CHLORINE added either in the form of a gas or as one of the commercially available high test hypochlorites is unquestioniably the most widely used agent for the disinfection of swimming pool water. In recent years bromine has been suggested for this purpose and equipment for its continuous feeding is commercially available, but to date it has found relatively little acceptance. Chlorine, however, as a disinfecting agent for swimming pool water has certain disadvantages. When applied to water it first reacts with ammonia, ammonium compounds, and other nitrogenotis compounds which may be present to form chloramines. When added in a concentration sufficient to destroy these compounds the process is termed breakpoint chlorination and any chlorine remaining after these compounds have been destroyed is called chlorine residual. Chlorine present in water in the form of chloramines is called chlorine and measured residuals are termed combined chlorine residuals. Within the preferred pH range of swimming pool water, namely 7.2-7.8, monochloramine is the main compound present. Numerous investigators, notably Wattie and Butterfield' have shown that the ability of chloramines to destroy bacteria is far less than that of free available chlorine. These investigators demonstrated that in chlorine-free, chlorine demand-free water of pH 7.8 some Escherichia coli survived after 120 minutes' exposure to water containing 0.30 ppm of chloramine and at pH 8.5, some E. coli survived for 240 minutes at the same chloramine concentration, namely 0.30 ppm. In contrast, no E. coli survived after five minutes' exposure to water containing only 0.07 ppm of free chlorine at pH 7.8 and at pH 8.5 no E. coli survived after 10 minutes' contact with water containing 0.07 ppm of free chlorine. The statement is commonly made that free chlorine is approximately 30 times as effective as chloramines in bactericidal efficiency. Also, when chlorine is added in an amount sufficient to destroy ammonia and other nitrogenous compounds present in the water, there is formed nitrogen trichloride which has a distinctive odor and may cause eye and nose irritation to some bathers. It has been shown that the bactericidal activity of free chlorine is due almost entirely to hypochlorous acid formed by its reaction with water. Since at high pH values this acid is neutralized to form the hypochlorite ion, the bactericidal efficiency of chlorine decreases steadily as the pH of the water increases.