Chromium (VI) biotransformation by beta- and gamma-Proteobacteria from natural polluted environments: a combined biological and chemical treatment for industrial wastes.

The high solubility of Cr(VI) in aqueous systems, together with carcinogenic and mutagenic effects on living organisms, make industrial effluents receive specific treatments for Cr(VI) elimination. Biotreatments, based on biotransformation of Cr(VI) to Cr(III) which is immobilized as Cr(OH)(3), are the most effective methods for the removal of Cr(VI) concentrations below 2mM. The aim of our study is the application of pure or mixed bacterial cultures for Cr(VI) biotransformation followed by chemical flocculation of Cr(OH)(3) as a combined treatment for industrial wastes. Pseudomonas veronii 2E, Delftia acidovorans AR, Klebsiella oxytoca P2 and Klebsiella ornithinolytica 1P, isolated from polluted environments showed a decrease from 38.83 to 74.32%, in 0.05 mM of initial Cr(VI). As revealed DGGE experiments, P. veronii 2E and K. ornithinolytica 1P could develop together in cocultures and in these conditions a 72.88% of Cr(VI) present was removed. Although the pH of the cultures was 8, no Cr(OH)(3) sediment was detected. The results of total chromium quantification support this observation. The precipitation of Cr(III) was induced using different commercial flocculants. Best yields were obtained using Na(2)CO(3) 0.1M, which allowed the flocculation of almost 100% of Cr(III) present. This combined treatment would be an economical and ecological way to remove Cr(VI).