Microbial chromium (VI) reduction

This review was conducted to describe the microbial reduction of hexavalent chromium [Cr(VI)] in general and a potential for biological treatment of Cr(VI)-containing wastes in particular. Cr(VI) is the highest oxidation state of the metal chromium, which is widely used in various industries. Chromate (CrO42-) is the prevalent species of Cr(VI) in natural aqueous environments and is the major pollutant from Cr-related industries. Cr(VI) exhibits inhibitory effects on biological wastewater treatment processes. Several microorganisms, however, have been found to be able to resist and/or reduce Cr(VI) within a wide range of Cr(VI) concentrations. The microbial Cr(VI:) reduction activities are either plasmid-or membrane-associated phenomena. Factors affecting microbial Cr(VI) reduction, including biomass concentration, initial Cr(VI) level, carbon source, pH and temperature, oxidation-reduction potential, oxyanions and metal cations, are discussed. The kinetic models for Cr(VI) reduction are described. Biological reduction of Cr(VI) demonstrates some potential as an innovative technology for remediation of Cr(VI)-contaminated environments, More mixed culture studies are needed to develop the proper biological reactor systems prior to field tests. In addition, more comprehensive kinetic models should be developed as a basis for engineering design and operation of biological Cr(VI)-removal processes.