Removal of Chloroform from Drinking Water

The overall objective of this investigation was to evaluate via laboratory experiments the technical feasibility of reducing trihalomethane levels in drinking water. Special attention was directed at the removal of chloroform since: (a) it is the only trihalomethane which has been shown to be carcinogenic in animal tests; and (b) this compound generally comprises the largest fraction of the total trihalomethane content of chlorinated waters in Kentucky. Trihalomethanes are present in municipal drinking waters due to the reaction of free chlorine with naturally occurring compounds, collectively called precursors . A variety of treatment processes and potential modifications (or additions) to existing treatment facilities were evaluated for precursor and trihalomethane removal. In-plant modifications which could be implemented at existing treatment facilities were evaluated initially since they require a minimal amount of capital expenditure and could be implemented within a short time frame. Unit treatment operations studied for precursor removal included: settling, alum-polymer coagulation, precipitive softening, ion-exchange softening. rapid sand filtration, adsorption with both powdered and granular activated carbon. and treatment with ozone and chlorine dioxide. A survey of the trihalomethane levels at fifteen of Kentucky\u27s larger water utilities was completed. While not a part of the original scope of this project, this information should assist local water utilities and health officials in assessing the State\u27s current trihalomethane situation. Additional field studies were completed at two of Kentucky\u27s water utilities to provide plant-scale data on: (a) the effectiveness of a shallow bed of granular activated carbon in removing trihalomethanes; (b) the reduction of trihalomethane levels by moving the point of pre-chlorination; and (c) the reduction in the formation of trihalomethanes during precipitive softening by converting free chlorine to chloramines prior to the addition of lime and soda ash. Results from both field and laboratory studies indicate that water utilities can markedly reduce the level of trihalomethanes currently in drinking water. Such reductions can be made by a variety of approaches which include alteration of disinfection practices, in-plant modifications to enhance precursor removal, and addition of new treatment processes such as carbon adsorption, ozonation and so forth. Only granular activated carbon adsorption appeared capable of completely removing precursor compounds and thereby eliminate the subsequent formation of trihalomethanes upon chlorination