Pilot studies of hexavalent chromium removal in the city of Glendale water supply

Public concern regarding the health effect of hexavalent chromium (Cr(VI)) in drinking water, coupled with the State of California's regulatory mandate, has encouraged the investigation of treatment technologies to remove Cr(VI) to concentrations well below the current federal and state total chromium standards. Various Cr(VI) treatment technologies have been successfully applied to industrial waste water treatment in which chromium concentration was in the mg/L range. Unfortunately, studies of low-level Cr(VI) removal from drinking water were quite limited. This dissertation presents a number of bench- and pilot-scale experiments aimed at removing Cr(VI) from Glendale groundwater to very low levels.;Several ion exchange technologies were first evaluated, including strong and weak base anion exchange resins, in both column and reactor configurations. The strong base anion exchange (SBA) resins in column configuration demonstrated a more consistent Cr(VI) removal performance than a reactor-based resin system. The best-performing column SBA resins could process 1900 BV of water before reaching 5 mug/L breakthrough while one weak base anion exchange (WBA) resin demonstrated a much higher Cr(VI) removal capacity (38,000 BV before 5 mug/L breakthrough). Residual management issues, including resin regeneration, brine stream minimization, and residuals characterization, were also addressed.;WBA resins were specifically investigated next because of the extraordinary Cr(VI) removal capacity shown in the previous study. Six WBA resins were first screened using the bench-scale isotherm test. Two resins with the highest Cr(VI) removal capacity were then tested in mini and pilot-scale columns to determine their removal performance under flow-through conditions. Testing results confirmed the high Cr(VI) removal capacity of both resins. Spent resins were further probed to determine their mechanism behind Cr(VI) removal. Oxidation-reduction was found to play a role in both WBA resins.;The last part of the dissertation describes a pilot-scale reduction/coagulation/filtration (RCF) system for Cr(VI) removal. The treatment process consisted of reduction of Cr(VI) to Cr(III) using ferrous sulfate followed by coagulation and filtration. Results indicated that the technology could effectively reduce influent Cr(VI) concentrations of 100 mug/L to below detectable levels and remove total Cr (Cr(VI) plus Cr(III)) to less than 5 mug/L under optimized conditions.