Chapter 10 : Microbial Reduction of Chromate

Abstract:

Chromium is one of the most widely used metals in industry. In addition, trivalent chromium( Cr(III)), is an essential trace element necessary for glucose and lipid metabolism and for the utilization of amino acids. Current treatment techniques for chromium-containing wastes generally involve aqueous reduction of hexavalent chromium (Cr(VI)) to Cr(III) by using a reducing agent at lowered pH with subsequent adjustment of the solution pH to near-neutral ranges to precipitate the less soluble Cr(III). Many facultative anaerobes are capable of reducing Cr(VI) to Cr(III) under appropriate conditions. Chromium-reducing bacteria may utilize a variety of organic compounds as electron donors for chromium reduction. The toxicity of Cr(VI) toward Cr(VI) reduction may be illustrated by the finite capacity of cells. The ability of an enzyme-based kinetic model to analyze Cr(VI) reduction was further demonstrated with two other strains, D. vulgaris and P. ambigua, reported in the literature. The model illustrates an important characteristic of microbial Cr(VI) reduction. The electron donors known for Cr(VI) reduction are generally limited to nontoxic aliphatic compounds, mainly low-molecular-weight carbohydrates, amino acids, and fatty acids. Recent work has revealed the potential of using Cr(VI)-reducing microorganisms for detoxifying Cr(VI)-contaminated environments or for treating Cr(VI)-containing wastes, even if the biochemical mechanisms of Cr(VI) reduction are not yet fully understood. Recent success in using a biofilm reactor for continuous reduction of Cr(VI) may have shed some light on methods for the biological treatment of Cr(VI)-containing wastes.