AWWA ACE56356

To minimize disinfection byproduct (DBP) formation three optimization options are available to conventional treatment plants that chlorinate prior to or at the rapid mix and include: lower the level of chlorine dosed at the rapid mix and re-chlorinate; move the point of chlorination to after the sedimentation basin; or, switch to a different pre- disinfectant/oxidant. However, implementing these optimization objectives cannot compromise the pathogenic barrier achieved by effective filters. The objectives of this study are to: assess and evaluate the conditions under which optimizing preoxidation is effective in controlling DBPs; and, determine the conditions under which preoxidation impacts filter performance. Tests were conducted with a pilot-scale system. Results indicated that lowering the pre-chlorination dose and re-chlorinating after the sedimentation basin such that a target distribution system residual (1 mg/L at 24 hours) is maintained, yielded lower chlorine consumed (up to 50%) and lower total trihalomethanes (TTHMs) formed after 24 hours (up to 29%). Two aspects of filter performance were monitored: the ripening period; and, steady-state turbidity. For all dose scenarios, steady-state turbidity averaged 0.06 ntu. Trends in increasing steady-state turbidities were observed as the preoxidant dose location for chlorine was moved from the rapid mix to mid-flocculation to post sedimentation. Chlorine also yielded lower steady state turbidities compared with chlorine dioxide and potassium permanganate dosed at the rapid mix. Includes 11 references, tables, figures.