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Feature wateronline.com ■ Water Online The Magazine 14 pressure vessel(s), where the arsenic adsorbs onto the media. As it starts to lose its adsorption capability, the media is replaced with new, virgin media. The new process features upflow regeneration utilizing 4 percent caustic solution (pH of 13) to strip the arsenic off the media. A second step, neutralization, injects 93 percent sulfuric acid into the flow stream to lower the pH of the treated water. The resulting hazardous-waste effluent must be handled appropriately, whether sent into the public sewer system (if available), treated on-site, and/or hauled offsite. Equipment requirements for Twentynine Palms were two HDPE tanks (3,200 gal) to collect wastewater, a tank (1,000 gal) and pump for the caustic solution, an acid-dosing pump, and a pH meter. Twentynine Palms also underwent minor pipe modifications to the existing treatment system, including plumbing for upflow and downflow application of the reagent, before regeneration could begin. The Twentynine Palms Experience Located in the Mojave Desert in Southern California, San Bernardino County, the Twentynine Palms Water District covers roughly 86 square miles and serves a population of approximately 17,800. When the updated MCL came out, the water district had three wells that were above the allowable limit. Two were shut down because of their age — "It wasn't worthwhile treating those wells," said Kolisz — and one was treated with Bayoxide E33 adsorptive media as part of a conventional use-and-replace treatment program. Raw water at the site in question, Well 11, averages 16 µg/L of arsenic. Though Twentynine Palms stayed in compliance by reducing arsenic below 10 µg/L, it was a consistently expensive endeavor. Kolisz, the operations manager both then and now, recalled the issue: "We put the system online, and the media wasn't performing as expected. We weren't getting the bed volumes that we thought we would. It prompted us to replace the media more often, which was a significant cost." The EPA and Battelle, having proved media regeneration in a lab environment, sought out Twentynine Palms to pilot- test the process in the field at full scale. The treatment system consisted of two vessels, each with 69 ft 3 of media. One vessel was set up to regenerate the spent media, while the other vessel's media was replaced with virgin media. To say the test results were positive is an understatement. The cost savings came through as expected, but the performance of the regenerated media was eye-opening. Despite the somewhat harsh process of removing the arsenic from the media, the regenerated media showed zero signs of degradation after use; in fact, it performed better on its second run, outshining even the virgin media. Kolisz explained that this was likely related to oil residue originating from the oil-lubed vertical turbine shaft pump that interfered with, or "blinded," the media. The caustic used to strip the arsenic off the media for regeneration essentially cleaned it of everything, thus improving performance. Today, Twentynine Palms continues to regenerate media at the 400-GPM Well 11 site — now served by two parallel vessels — removing 90 percent of accumulated arsenic with each regeneration (and still no indication of media breakdown). The efficient arsenic-removal rate allows some raw water to be bypassed and blended with the treated water, while still staying far below the regulated limit. Mitigating Factors To Consider There are two major responsibilities to recognize before taking on media regeneration: operator training and wastewater disposal. A main reason Twentynine Palms was chosen for the EPA's demonstration program was the utility's familiarity and training with adsorptive media regeneration — not for arsenic removal, but for fluoride removal. Twentynine Palms regenerates activated alumina to remove naturally occurring fluoride, so it had comparable equipment and training in place. Pressure vessels at Twentynine Palms The cost savings came through as expected, but the performance of the regenerated media was eye-opening. 1 4 _ V E R T _ 0 5 1 4 C l e a n w a t e r _ F e a t u r e _ D G . i n d d 2 14_VERT_0514 Cleanwater_Feature_DG.indd 2 4 / 2 1 / 2 0 1 4 3 : 0 0 : 5 0 P M 4/21/2014 3:00:50 PM