Full-scale demonstration testing of hexavalent chromium reduction via stannous chloride application
- Tarrah Henrieb(Author),
- Sarah Plummerb(Author),
- John Ortaa(Author),
- Steve Bigleyd(Author),
- Craig Gormanc(Author),
- Chad Seidelc(Author)
- aDepartment of Chemical and Environmental Engineering, University of California, Riverside,
- bCorona Environmental Consulting,
- cCorona Environmental Consulting,
- dCoachella Valley Water District
Abstract
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.