AWWA ACE65182

This poster paper presents an effort bt the Medford Water Commission (MWC) to evaluate alternatives to chlorine gas disinfection systems at the Robert A. Duff Water Treatment Plant (Duff WTP) and the big Butte Springs Facility (BBS). The primary alternative examined was sodium hypochlorite, either as a 12% bulk solution or 0.8% solution generated from salt. Hypochlorite raises the pH of the water and could potentially affect the optimum dose of polyaluminum chloride (PACl) for turbidity removal. The Duff WTP is not currently operated in an "enhanced" coagulation mode for total organic carbon (TOC) removal. The diurnal pH change and its impact on the coagulation system were also considered, since alum is more sensitive to pH changes than PACl. Bench scale experiments were conducted on June 15 - 17, 2005 to investigate the water quality impacts resulting from sodium hypochlorite use instead of chlorine gas at the Duff WTP and BBS. The bench-scale results verified results from the Rothberg, Tamburini & Windsor (RTW) computer model. Additional testing was also conducted on August 19, 2005. Testing included pH adjustment as a function of sodium hypochlorite and coagulant addition, bromate testing of on-site generated and bulk sodium hypochlorite, and pH control using carbon dioxide to create a favorable coagulation system. Simulated Distribution System (SDS) tests were performed to evaluate the disinfection byproduct (DBP) formation at different pH values, and an evaluation of the contact time (CT) requirements at various pH values and the impact of the pH changes on the distribution system were also evaluated. Bench scale testing goals are listed, and figures charting the pH response to sodium hypochlorite are provided. Includes table, figures.