Removal of chlorite and chlorate ions from water using granular activated carbon

Bench scale column experiments were performed to determine the ability of granular activated carbon (GAC) to remove chlorite ion (ClO 2 −, the major by-product of chlorine dioxide, and chlorate ion (ClO 3 −, with or without natural organic matter, and under various operational conditions. Operational variances included the effect of pH, hydraulic loading, influent concentration and GAC particle size. Initially, all influent ClO 2 − was reduced to ClO − by GAC, but later carbon capacity for ClO 2 − reduction was decreased and ClO 2 − breakthrough was observed. Chlorite ion reduction was improved by decreasing the natural organic matter concentration, decreasing pH, decreasing hydraulic loading, decreasing GAC particle size and increasing temperature. All other parameters were maintained constant, the most effective chlorite ion removal occurred at pH 5. The results may be of interest to many water utilities, which use activated carbon for removal of organic compounds and in filter adsorbers replacing anthracite coal. There was no formation of chlorate ion in the GAC-chlorite system in the dark. Chlorate ion was not reduced by GAC, but was only physically and reversibly sorbed.