Regenerating an Arsenic Removal Iron‐Based Adsorptive Media System, Part 2: Performance and Cost

Abstract

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. ...

Regenerating an Arsenic Removal Iron‐Based Adsorptive Media System, Part 1: The Regeneration Process

“…Recycling of some of the wastewater was also proposed by the TPWD to further reduce the quantity of wastewater for disposal. The plan consisted of adding ferric chloride to wastewater to precipitate out the arsenic and recycle the supernatant to the front of the plant at very low flows (5–20 gpm); additional details of this activity can be found in the second article of this two‐part series (see Sorg et al 2017 on page 25). Because of California's rather stringent monitoring requirement, the wastewater was again hauled off‐site.…”

“…Ultimately, these solutions and solids were also disposed of at an off‐site disposal facility. More details of the handling of wastewaters produced from the second and third regeneration are presented in the second article in this series (Sorg et al 2017).…”

Regenerating Iron-Based Adsorptive Media Used for Removing Arsenic from Water

“…The obtained iron media can be used for removing As from water based on the mechanism of adsorption of arsenic on ferric hydroxides, a chemical exchange that by its nature is reversible. Various studies have found that a classic three-step regeneration process of (1) backwashing the iron media, (2) caustic regeneration, and (3) acid neutralization conditioning has been shown to be effective in removing As and other contaminants absorbed by the iron media [22,23]. Hence, the study of the reactivation process and the subsequent development of the design of the novel technological plant presented here were based on experiences conducted by the international scientific community, in particular by the US Environmental Protection Agency, both as laboratory tests and small pilot plants on real-scale interventions.…”

“…ditioning has been shown to be effective in removing As and other contaminants abso by the iron media [22,23]. Hence, the study of the reactivation process and the subseq development of the design of the novel technological plant presented here were base experiences conducted by the international scientific community, in particular by th Environmental Protection Agency, both as laboratory tests and small pilot plants on scale interventions.…”

Patterns of arsenic release in drinking water distribution systems

“…In three overlapping phases (Rounds 1, 2, and 2a), the Arsenic Demo evaluated full‐scale arsenic removal technologies at 50 small water systems located in 26 states between 2001 and 2011 (Sorg, ). Key conclusions from the Arsenic Demo, including treatment technology effectiveness, and costs, are summarized elsewhere (e.g., Chen, Wang, Lytle, & Sorg, ; Lytle et al, ; Sorg, , ; Sorg & Chen, ; Sorg, Chen, Wang, & Kolisz, ; Sorg, Kolisz, Chen, & Wang, ; Sorg, Wang, & Chen, ; Wang & Chen, ). Final reports for each of the 50 systems were also made public through the Arsenic Demo website (USEPA, ).…”