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The best available technologies for hexavalent chromium [Cr(VI)] treatment can be cost prohibitive and operationally complex. Direct stannous [Sn(II)] chloride application to reduce Cr(VI) to trivalent chromium is an alternative treatment approach that could substantially decrease treatment costs. A full‐scale demonstration was conducted at the Coachella Valley Water District to investigate the ability of Sn(II) to reduce Cr(VI) in a chlorinated groundwater system. An average Sn(II) dose of 0.5 mg‐Sn/L, which corresponds to ~7.3 times the stoichiometric dose ratio for Cr(VI) reduction, was able to maintain Cr(VI) at <10 μg/L throughout the distribution system over a 30‐day period. Tin (Sn) and chromium (Cr) concentrations decreased with increasing distance from stannous feed locations, suggesting accumulation in the distribution system. Distribution system pipe‐scale analysis after the demonstration found the presence of Sn and Cr in pipe scales; however, minimal Sn and Cr release was observed during main flushing at the end of the demonstration.

Regeneration of strong base anion (SBA) exchange resin produces concentrated and hazardous brine. In this research, one alternative regenerant and two brine treatment options were investigated to reduce the hazardous characteristics of the brine. These options included replacing sodium chloride with sodium bicarbonate as the regenerant, using ferrous sulfate (FeSO4) to reduce/coagulate hexavalent chromium (CrVI) in the brine, and applying weak base anion (WBA) exchange resin and chemical reductive media (CRM) to adsorb/reduce CrVI. It was found that bicarbonate was as effective as chloride in regenerating chromium‐saturated resins, and the affinity of the bicarbonate‐form resin for chromium was similar to that of the chloride‐form resin. It was observed that FeSO4 applied at doses close to the stoichiometric ratio achieved almost complete removal of total chromium from the SBA brine. In column tests, two CRM exhibited more than 20 times greater removal capacity for total chromium than did the WBA exchange resins.

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