Adsorptive media technology is frequently used by small water systems to remove arsenic because of its simplicity and efficiency. Current practice is to replace the media when it no longer reduces arsenic below the maximum contaminant level of 10 µg/L that the US Environmental Protection Agency has set for drinking water. Media replacement typically accounts for approximately 80% of the total operational and maintenance costs. One potential option to reduce the cost is onsite regeneration and reuse of the media. To evaluate the regeneration option, three consecutive regeneration studies were conducted on a full-scale adsorptive media system. This article, the first of a twopart series, describes the regeneration process and its efficacy in stripping arsenic and other contaminants from exhausted media. Study results found that a threestep regeneration process of media backwash, caustic regeneration, and acid neutralization conditioning proved effective for stripping arsenic and other contaminants from the exhausted media. 2017

In the first article (Sorg et al. 2017) in this two-part series, results of three regeneration studies were presented. That study highlighted a three-step regeneration process of media backwash, caustic regeneration, and acid neutralization conditioning to strip arsenic and other contaminants from exhausted granular ferric oxide (GFO) media 1 in the arsenic removal treatment system at the Twentynine Palms Water District (TPWD) in California.This article, the second of two, presents performance data on the treatment system to remove arsenic following the three regeneration studies (detailed in Sorg et al. 2017) and the two subsequent studies conducted by TPWD. The authors also look at the estimated cost savings of each regeneration over media replacement. MATERIALS AND METHODSArsenic treatment system and operation. The TPWD arsenic removal system consists of two 5 ft-diameter adsorption vessels in parallel (tanks A and B); detailed design information for the system can be found in the first article of this series (Sorg et al. 2017). To extend the life of the adsorptive media, TPWD blends raw well water with the treated water; the blending ratio decreases with the increasing arsenic concentration of the system's treated water. The US Environmental Protection Agency (USEPA) has set a maximum contaminant level (MCL) for arsenic of 10 µg/L; the goal of the TPWD blending water process is to provide distribution water with an arsenic concentration of <8 µg/L. The decision of when to regenerate one tank of media was generally determined by the arsenic concentration of the finished blended water and not that of the adsorptive media effluent. Consequently, regeneration of the adsorptive media was carried out before the media had reached exhaustion (arsenic effluent at 10 µg/L).Data and sample collection. Because the first three regenerations (studies) were conducted with assistance from USEPA and its contractor (Battelle), monitoring of system performance after these three regenerations was supported by USEPA to collect more extensive performance data than what could be accomplished with only the TPWD resources.Immediately following system startup after each of the three regeneration studies, an effluent grab sample was collected of the well water and the effluents from tanks A and B. The same three samples and a blended finished water sample were collected daily during the first week of operation and then weekly for weeks two, three, and four. After week four, this set of four samples was collected weekly along with a distribution water Peer ReviewedReplacement of exhausted, adsorptive media used to remove arsenic from drinking water accounts for approximately 80% of total operational and maintenance costs of this commonly used small system technology.Results of three full-scale system studies of an onsite media regeneration process (discussed in the first article of this two-part series) showed it to be effective in stripping arsenic and other contaminants from a granular ferric oxide (GFO) exhausted adsorptive media. ...