The effectiveness of localized treatment for meeting the Stage 2 Disinfectants and Disinfection Byproducts Rule (DBPR) is examined. Localized treatment is an approach where only the portion of water in the distribution system that exceeds the DBPR is treated. A pilot plant was installed
at a reservoir site at an extremity of the Las Vegas Valley Water District's (LVVWD) distribution system. The pilot plant consisted of two treatment trains: one with air stripping followed by granular activated carbon (GAC)/biologically active carbon (BAC), and the other with only GAC/BAC.
It was found that air stripping removed 75-85% of TTHMs and that BAC removed most of the HAA5s. GAC produced varying amounts of TTHM removal based on the number of bed volumes treated. The pilot plant was operated for 12 months to capture seasonal differences in treatment effectiveness. Simulated
distribution system (SDS) testing was conducted on blends of treated and reservoir water. Results for LVVWD water indicated that with a blend of only 25% treated water and 75% reservoir water, TTHM concentrations could be maintained below 80 ug/L, even with a contact time of 7 days after re-chlorination.
The SDS testing produced TTHM and HAA5 Formation Potentials that are similar to results using empirical equations developed by the EPA. SDS testing was also conducted on waters from the Regional Water Authority of Connecticut and the City of Phoenix, Arizona. The results of pilot and SDS
testing were used to construct a spreadsheet model for use in estimating DBP removal with treatment and DBP reformation with re-chlorination. The model was linked with the hydraulic model of the LVVWD Distribution System. A cost estimating model was also developed for use with the treatment
and reformation model in determining if localized treatment might be a cost effective alternative to treating the entire supply at a centralized location. For this study, it was found that localized treatment and indeed be a viable approach for meeting the Stage 2 DBR requirements.
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