The potential for biological treatment of Cr (VI)- polluted wastewaters has attracted increased interest, because this alternative is more efficient and less expensive than conventional physicochemical treatments. In this work, a microbial enrichment capable of tolerating and reducing high Cr(VI) was isolated. The kinetic parameters of the Cr(VI) reduction process indicate that the enrichment culture has a significant potential for bioremediation of Cr(VI)-laden wastewaters.
Hexavalent chromium [Cr(VI)] is the major chromium species used in industrial processes, including chrome plating, petroleum refining, manufacture of pigments, leather tanning, wood processing, and so on (Salunke et al., 1998). Improper handling and storage of chromium-laden effluents or wastes has led to Cr(VI) contamination of surface water, groundwater, soil and sediment (Desjardin et al., 2003), which has posed acute and chronic health risks to animals and humans, since Cr(VI) is acutely toxic, mutagenic, carcinogenic, and teratogenic (Marsh and McInerney, 2001; McLean and Beveridge, 2001). Focusing on its toxicity and exposure potential, the United States Environmental Protection Agency (USEPA) lists hexavalent chromium as a priority pollutant (Smith et al., 2002).
The biological reduction of hexavalent chromium to trivalent chromium [Cr(III)] has attracted increased interest, since this process may not only relieve the toxicity of chromium acting on living organisms [Cr(III) is 100 times less toxic and 1000 times less mutagenic than Cr(VI)], but it also aids in the precipitation of chromium at near-neutral pH [mainly as Cr(OH)3] for further physical removal (Wang, 2000). This promising technique appears to be efficient, environmentally friendly and cheaper than currently used processes (Chardin et al., 2002).
However, the potential of biological treatment of Cr(VI)-contaminated waste is limited because microorganisms lose viability in the presence of high concentrations of Cr(VI). The isolation of microorganisms capable of reducing high Cr(VI) concentrations would be therefore very useful.
The main purposes of this work were to obtain an enrichment consortium capable of tolerating and reducing very high Cr(VI) concentrations and to evaluate its potential for reductive chromate detoxification using glucose as a widely available and economical electron donor.