In chlorination, chlorine's reaction with ammonia forms chloramines, greatly reducing its bactericidal and virucidal effectiveness. The biocidal activity of monochloramine is only 0.02 - 0.01 times as great as that of free chlorine. Typical ammonia concentrations found in secondary sewage range from 5-20 ppm, which is about an order of magnitude greater than the amount needed to form monochloramine from normal chlorination dosages (which requires about 5-10 ppm). Therefore, monochloramine is the major active chlorine constituent in chlorinated sewage plant effluents. In contrast, BrCl ammonia reactions produce the major product bromamines. Bromamines have disinfectant characteristics which are significantly different than chloramines.
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