The hexavalent chromium Cr (VI) and sulfate concentrations in some groundwater sources used for drinking water in Birjand, the capital of Southern Khorasan Province, Iran, are greater than the established maximum concentration levels (MCLs). In this work, a nanofiltration system was examined as a promising method for the simultaneous removal of Cr (VI) and sulfate from groundwater. The effects of operating pressures (2–10 bar) on Cr (VI) (0.1–0.5 mg/l) for and sulfate (800 mg/l) were investigated. Experimental results in Birjand drinking water indicated that a better rejection of Cr (VI) (96%) was obtained at basic pH and at an optimal pressure of 4 bar. In addition, an increase of sulfate (up to 600 mg/l) led to a decrease in the retention of hexavalent chromium at 4 and 8 bar, respectively. We did mass balance analysis to show the fate of the rejected ions by membrane. On the basis of our results, NF90 had much more efficient removal (R>94%) for all monovalent and divalent anions and cations and appeared to be applicable for the removal of Cr (VI) and sulfate from the Birjand drinking water.
Keywords: brackish water, hexavalent chromium, nanofiltration, rejection, sulfate