MICROBIAL CHROMIUM(VI) REDUCTION

This review was conducted to describe the microbial reduction of hexav alent chromium [Cr(VI)] in general and a potential for biological trea tment of Cr(VI)-containing wastes in particular. Cr(VI) is the highest oxidation state of the metal chromium, which is widely used in variou s industries. Chromate (CrO42-) is the prevalent species of Cr(VI) in natural aqueous environments and is the major pollutant from Cr-relate d industries. Cr(VI) exhibits inhibitory effects on biological wastewa ter treatment processes. Several microorganisms, however, have been fo und to be able to resist and/or reduce Cr(VI) within a wide range of C r(VI) concentrations. The microbial Cr(VI:) reduction activities are e ither plasmid-or membrane-associated phenomena. Factors affecting micr obial Cr(VI) reduction, including biomass concentration, initial Cr(VI ) level, carbon source, pH and temperature, oxidation-reduction potent ial, oxyanions and metal cations, are discussed. The kinetic models fo r Cr(VI) reduction are described. Biological reduction of Cr(VI) demon strates some potential as an innovative technology for remediation of Cr(VI)-contaminated environments, More mixed culture studies are neede d to develop the proper biological reactor systems prior to field test s. In addition, more comprehensive kinetic models should be developed as a basis for engineering design and operation of biological Cr(VI)-r emoval processes.