Pilot Testing Strong Base Anion Exchange for CrVI Removal

Abstract

California, the first state in the nation to regulate hexavalent chromium (CrVI) in drinking water, has set a maximum contaminant level (MCL) of 10 µg/L. To comply with the MCL, a California utility conducted extensive pilot studies to determine the best‐performing ion exchange resin, empty bed contact time (EBCT), and hydraulic loading rate (HLR). The CrVI removal capacities of four strong base anion exchange resins were tested at seven wells. Results showed that between 12,000 and 37,000 bed volumes of treatment can be expected before an 8‐µg/L breakthrough threshold. HLR was shown to have little effect on CrVI removal within the range tested (7.5 to 30 gpm/ft 2 ), whereas longer EBCTs (>45 s) appeared to improve performance. The presence of co‐occurring anions in the raw water—namely, sulfate and nitrate—had substantial effect on the resin's chromium loading capacity.