AWWA ACE94161

Research has shown that reducing organic carbon concentrations prior to chlorine disinfection reduces the concentration of total THMs, the sum of the concentrations of the four individual species. Although the total THM concentration decreases with removal of organic carbon, the concentrations of the more brominated THMs can increase. If these more brominated byproducts are particularly hazardous, the overall cancer risk could increase as organic carbon concentrations at the point of chlorine application are reduced, thereby undermining the proposed disinfection byproduct control strategy. Alternatively, if the potencies of these more brominated THM species are less severe but still high relative to their chlorinated counterparts, organic carbon removal could result in little or no risk reduction. Considering the above concerns, a risk modeling effort was undertaken to evaluate the byproduct control strategy of removing organic carbon prior to disinfection in water treatment plants. Three primary objectives were identified for investigation: determine how cancer risks change with various degrees of organic carbon removal; evaluate the impact of water quality on potential risk reduction; and estimate the cost-effectiveness of enhanced coagulation in reducing cancer risk. To accomplish the above objectives a methodology was established to evaluate the performance of treatment upgrade alternatives on the basis of cancer risk reduction achieved.