Localized Treatment for Disinfection By-Products

Abstract

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.

Not your granddad's disinfection by‐product problems and solutions

“…The bed lives for MCAA, DCAA, trichloroacetic acid, and chloroform were reported at 2, 20, 200, and 100 days, respectively, at an EBCT of 20 min (Tung et al, 2006). These results were similar to those reported by Johnson et al (2009). These short bed lives imply that it is generally impractical for water systems to adopt the carbon adsorption technique because of too‐frequent carbon regeneration.…”

“…Localized water treatment. Localized water treatment includes storage tank aeration, GAC adsorption, and biologically active carbon (BAC) filtration (Brooke & Collins 2011; Johnson et al, 2009; Sherant et al, 2007). These treatment processes can be used for treating DBP hot spots in large distribution systems and consecutive systems.…”

“…Some utilities have considered installation of satellite GAC or BAC facilities to control areas of high DBPs that threaten regulatory compliance. On the basis of the carbon type and EBCT, GAC has a bed life of 3–6 months for THMs (Johnson et al, 2009; McGuire & Suffet, 1978a; Tung et al, 2006). For HAAs, much shorter bed lives are expected for monochloroacetic acid (MCAA) and dichloroacetic acid (DCAA).…”