AWWA WQTC58983

In order to meet the Stage 1 and future Stage 2 Disinfectant and Disinfection Byproducts Rules, the Cobb County-Marietta Water Authority has completed an intensive pilot-scale evaluation of advanced treatment technologies for disinfection byproduct (DBP) precursor removal at the 72-million-gallons-per-day (mgd) Wyckoff water treatment plant (WTP). The authority had observed elevated DBP levels in the distribution system, and due to the fact that several consecutive systems purchase water from multiple sources and areas with extended hydraulic residence time, simple solutions such as decreasing chlorine dose or switching to chloramines were not options. The study was conducted over a 12-month period by the authority and its consultant, CDM, utilizing a two-train pilot-scale treatment plant. One train was used to simulate existing rapid mixing, flocculation, sedimentation, and filtration treatment processes to provide a baseline comparison, while the second train was used to evaluate the effect of adding various DBP precursor reduction technologies to the existing Wyckoff WTP treatment process train. Technologies evaluated in the study included pre-chlorine dioxide in lieu of prechlorination, pre- and intermediate-ozone/biofiltration, magnetically enhanced ion exchange (MIEX), and post-filter nanofiltration. Results of the study indicated the ability of the Wyckoff plant to significantly lower DBP levels to meet Stage 1 requirements by switching to chlorine dioxide as a pre-oxidant in lieu of prechlorination. Ozone/biofiltration did not have an incremental difference in the results for DBP precursor removal compared to pre-chlorine dioxide. Both pretreatment with MIEX and post-filter nanofiltration provided significant reduction in DBP precursors, allowing these technologies to be considered for future implementation to meet Stage 2 DBP requirements. Includes reference, tables, figures.