Low-Level Hexavalent Chromium Treatment Options

Book excerpt: In February 1999, the California Office of Environmental Health Hazard Assessment issued a Public Health Goal (PHG) for total chromium of 2.5 μg/L. The PHG, based on a 10^6 risk level for 0.2 μg/L hexavalent chromium [Cr(VI)], was 40 times less than the USEPA's contaminant MCL of 100 μg/L for total chromium [Cr(III) ] Cr(VI)]. The success of the movie Erin Brockovich, which popularized a groundwater chromium pollution lawsuit in Hinkley, California, sensitized the public to the health hazards of chromium in drinking water. In 2001, the California state legislature passed a bill requiring the California Department of Health Services to adopt an MCL for Cr(VI). All of these actions must be viewed from the perspective that, at the time, no technology had been demonstrated to be effective at treating chromium to concentrations consistent with the total chromium PHG or the Cr(VI) 10^6 risk level of 0.2 μg/L. The purpose of this report was to present the results of this partnership study, which included an analysis of chromium occurrence and co-occurrence, an evaluation of Cr(VI) removal technologies, and an examination of chromium oxidation and reduction chemistry. This study investigated nearly all of the potential methods of controlling Cr(VI) either through the use of technologies that remove Cr(VI) directly (adsorption, anion exchange, membrane filtration) or those that remove the reduced form of chromium, Cr(III) (precipitation with membranes or coagulation and precipitation with conventional or membrane filters). These technologies were investigated using laboratory-scale testing methods, including batch isotherm tests, bench membrane systems, flow-through mini-columns, and jar testing techniques. For most technologies, controlled water matrices were used to screen performance. Selected technologies were further assessed using natural groundwater matrices from the Los Angeles Department of Water and Power and the Glendale Water and Power groundwater facilities.