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In February 1999 the California Office of Environmental Health Hazard Assessment (OEHHA) issued a Public Health Goal (PHG) for total chromium of 2.5 ug/L. This is based upon a de minimus (10-6) risk level at 0.2 ug/L for hexavalent chromium (Cr(VI)). The PHG is 40 times less than the US Environmental Proteciton Agency's (USEPA) maximum contaminant level (MCL) of 100 ug/L for total chromium (Cr(III) + Cr(VI)). This action has directly impacted several California utilities and may ultimately have broad implications for utilities nationwide. While treatment technologies exist for the treatment of Cr(VI) in industrial wastewater, no drinking water Cr(VI) treatment technology has been demonstrated to reach the low levels recommended by the OEHHA. This paper summarizes the results of bench level experiments evaluating the performance of alternative reductants for the conversion of Cr(VI) to Cr(III) and investigating the fate of Cr(III) under distribution system conditions. The objectives of the project were to: compare the effectiveness of Cr(VI) reduction to Cr(III) using sodium metabisulfite, ferrous sulfate and stannous chloride as alternative reductants; and, investigate the kinetics of Cr(III) re-oxidation to Cr(VI) in the presence of free chlorine. Reduction experiments were performed by rapidly mixing the alternative reductants with 500ml of Cr(VI) contaminated groundwater. Aliquots were withdrawn at predetermined intervals and analyzed for Cr(VI) concentration. Re-oxidation experiments were performed by chlorinating previously reduced Cr(III) samples (the reduction was performed with SnCl2 at a 1.5 stoichiometric dose) and monitoring the formation of Cr(VI) as a function of time. All experiments were performed open to the atmosphere and at room temperture using the Cr(VI) contaminated groundwater. Hexavalent chromium was detected spectrophotometrically at 540 nm by derivativation with diphenylcarbazide. Includes 18 references, tables, figures.

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Edition: Vol. - No. Published: 06/16/2002 Number of Pages: 9File Size: 1 file , 580 KB