Removal of chromium using Rhizobium leguminosarum

The chromium (Cr(III) and Cr(VI)) removal capability of Rhizobium leguminosarum was checked by estimating the amount of chromium in the medium before and after inoculation. To determine the efficiency of R. leguminosarum in removal of chromium, the influence of physical and chemical parameters such as temperature, pH and different concentrations (0.1-1.0 mM) of trivalent (Cr(III)) and hexavalent (Cr(VI)) chromium were studied. The chromium removal in aqueous solution by different size of active and inactivated biomass and immobilized cells of R. leguminosarum in a packed-bed column was also carried out. Results showed that in a medium containing up to 0.5 mM concentration of both Cr(III) and Cr(VI), R. leguminosarum showed optimal growth. The maximum chromium removal was at pH 7.0 and 35°C. Active biomass removed 84.4 ± 3.6% of Cr(III) and 77.3 ± 4.3% of Cr(VI) in 24 h of incubation time. However, inactivated biomass removed maximum chromium after 36 h of incubation. Immobilized bacterial cells in a packed-bed column removed 86.4 ± 1.7% of Cr(III) and 83.8 ± 2.2% of Cr(VI) in 16 and 20 h of incubation time, respectively.