THE REACTION OF AQUEOUS FREE CHLORINE WITH ORGANIC COMPOUNDS ADSORBED ON GRANULAR ACTIVATED CARBON

The reaction of organic compounds with aqueous chlorine was examined before and after adsorption on an activated carbon bed. An extract of humic acid from peat soil was used as the organic compound in the first part of the study. The concentration of humic acid and chlorine were typical of those encountered in municipal water treatment plants. By using a mass balance on total organic halogen (TOX), it was determined that chlorine residual entering a carbon bed did not react with adsorbed organics, or organics present in the pore water, to produce additional amounts of TOX. In all cases the TOX recovered on the carbon and in the effluent from the carbon bed was equal to, or less than, the TOX which entered the bed in the influent. This is significant since chloro-substituted organics are often resistant to biological degradation and some may pose a health risk. Capillary and packed column gas chromatography were used to examine whether unique organic compounds were formed by the reaction of chlorine with adsorbed humic materials. At no time during the column runs were compounds found in the effluent from the columns that were not also found in the influent. Several dihydroxy and chlorinated dihydroxy benzenes were found in an extract of the carbon that were not found in the chlorinated humic acid influent and may have been formed on the carbon. A series of phenolic acids were used as the organic compounds in the second part of the study. These compounds are structural breakdown products of humic acids and have been shown to react with free chlorine in aqueous solution. When chlorinated in aqueous solution, the products were generally the mono and dichloro phenolic acids, the mono and dichloro decarboxylation products, and some unreacted starting material. When the solution of chlorine residual and phenolic acid was passed onto carbon, many additional compounds were found. Tentative identification from mass spectra alone, indicated a series of polyphenols and hydroxylated quinones. The predominant reactions at the carbon surface appeared to be decarboxylation, hydroxylation, demethylation of methoxy substituents, oxidation of polyphenols to quinones, and chlorine substitution reactions. The presence of these products suggests that reactions on carbon may proceed quite differently than reactions in aqueous solution. Many of the oxidized products formed from the reaction of chlorine and vanillic acid on carbon are identical to the reaction of chlorite and vanillic acid on carbon.