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Pilot Study and 12516 bed volumes. Effluent samples from GAC-loaded columns were tested for column flow rate, temperature, free chlorine, THMs, DOC, and UV254. This testing was done daily for the first eight weeks and then weekly for the last six weeks of the project. The simulated distribution system (SDS-THM) tests were performed on the effluent samples at 2016, 4020, 5748, 7758, 10494, and 12516 bed volumes. The OLC 12x40 GAC (coconut Figure 2: Reformation of TTHMs at two different temperatures for the Carbonair unit shell) showed very fast DOC breakthrough and nearly complete chlorine residuals after air stripping was minimal. breakthrough (90 to 100 percent) toward the end of Bench-scale studies were conducted to determine the the project. However, this coconut shell-based carbon, reformation potential of DBPs after rechlorinating the due to its internal structure very high in micropores, effluent from the air stripping system. The results dem- exhibited very high efficiency in THMs removal even onstrated that TTHM reformation occurs, and the forma- when DOC breakthrough was nearly complete. The tion levels in some instances exceeded the 80-ppb limit FILTRASORB 400-M (bituminous), on the other hand, between the 72-hour and 96-hour sampling points (Figure showed excellent DOC removal and relatively good 2). Several blending ratios were tested, and reforma- THM removal. This bituminous-based carbon, with the tion potential was the least for a blending ratio of 75:25 internal structure that contains more mesapores than (treated:untreated). the coconut shell-based carbons, exhibited balanced adsorption over a broad range of high (NOM and DOC GAC pilot studies: fragments) and low (THMs) molecular weight species. The pilot test system consisted of a GAC column The correlation between DOC and TTHMs adsorption apparatus from Batelle. The GAC column apparatus for coconut shell- and bituminous-based carbons is featured three glass columns connected in a parallel illustrated in Figure 3. The spikes in the removal of configuration allowing for simultaneous testing of DOC and TTHMs can be attributed to the varying multiple columns. Each column was 48" long with a 2" influent water quality. diameter. The GAC column apparatus was fastened to The simulated distribution system (SDS)-THM data a 4"x4" steel frame, which was anchored to the ground was evaluated against THM hold test data at 72 hours (cement slab) and equipped with the appropriate (three days) and 168 hours (seven days). For the first valves and flow meters. Two GAC sources were tested 4,000 bed volumes of the operation, the two carbons and evaluated in this project: FILTRASORB® 400-M, a removed THMs very efficiently at both 72 and 168 bituminous-based GAC; and OLC 12x40, a coconut shell-based GAC. Both FILTRASORB 400-M and OLC 12x40 are manufactured by Calgon Carbon Corporation. Influent water quality was monitored weekly for temperature, free chlorine, trihalomethanes (THMs), dissolved organic carbon (DOC), and UV-absorbing organic constituents (UV254) throughout the duration of the project. In addition, a THM hold test was performed on the influent samples Figure 3: TTHM and DOC removal percentages for GAC effluent (Left graph is for coconut shell-based GAC; at 0, 2016, 4020, 5748, 7758, 10494, right graph is for bituminous coal-based GAC) 20 wateronline.com ■Water Online The Magazine