The Bromination of Swimming Pools

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Abstract
A survey of the literature relating to the chemistry and disinfectant properties of free and combined bromine is presented and discussed in the light of the author''s work on this subject. At the pH values found in swimming pools free bromine exists on an equilibrium mixture of hypobromous acid and hypobromite ion, which react with ammonia to give a breakpoint reaction similar to that given by free chlorine but possessing a much greater reaction rate. Monobromamine has almost the bactericidal strength of free bromine. The pka for monobromine is 6.5, hence at pH values near 7.0 there is considerable monobromammonium ion present and this is considered to exert the strong bactericidal effect. By contrast monochloramine has a pka of less than 1.0, with virtually none of the ion present at pH 7. For analytical purposes both free and combined bromine react in the same manner as free chlorine with ortho-tolidine and ampero-metric titration. Free or combined bromine may be differentiated by addition of ammonium sulphate to the amperometric apparatus. With free bromine there is a large decrease in current, and with monobromamine only a small or no decrease; the titration is then performed as usual with phenylarsenoxide. Bromine has the advantage that break-point need not be attained to obtain good disinfection, and this feature may make bromine economical relative to chlorine.