[Reducing chloramines in drinking water]

Monochloramine is produced when drinking water containing ammonium is chlorinated. It has long been known that activated charcoal destroys monochloramine. However, exact data for the dimensioning of a dechloramination plant were lacking. Four different commercially available activated charcoals were characterized (size of particle, iodine number) and examined for their effectiveness in removing monochloramines. The degradation of monochloramine by active charcoal is based on a chemical reaction of first order between carbon and monochloramine. The types of activated charcoal considerably differ in terms of reaction velocity, due in part to the mean granular size. The final concentration of the monochloramines is influenced only by their length of stay in the activated carbon filter, the temperature and the inflow concentration. A mathematical model describes the dependence of the degradation rate of the monochloramines on various factors. With its aid a nomogram can be established with which, simply and quickly, the activated charcoal needed in a concrete case can be determined.