Reduction of hexavalent chromium by Bacillus cereus Cr4-1

Objective To study the reduction of hexavalent chromium (CrVI)by Bacillus cereus (B.cereus) Cr4-1.Methods Effects of temperature,pH,initial Cr(VI) concentration and shaker speed on hexavalent chromium reduction and the growth of B.cereus were explored with orthogonal tests.Nine common carbon sources were used in the bacteria culture and Cr(VI) reduction test in order to screen the optimum carbon source and electron donor.Transmission electron microscopy was employed to observe morphological changes of bacteria Cr4-1 before and after Cr(VI) reduction.Results The main factors influencing the growth of the bacteria were shaking speed and pH value.The main factors influencing the Cr(VI) reduction were initial Cr(VI) concentration and temperature.The better conditions for the bacterial growth and Cr(VI) reduction were the temperature of 35℃,pH value of 9,initial Cr(VI) concentration of 30 mg/L,and the shaking speed of 150 r/min.Sodium lactate was the best carbon source for bacterial growth and Cr(VI) reduction,followed by sodium pyruvate.Toxic effect of Cr(VI) on B.cereus Cr4-1 strain during Cr(VI) reduction process at the initial Cr(VI) concentration of 30 and 60 mg/L was observed with transmission electron microscope and the effect was positively correlated with the initial Cr(VI) concentration.Conclusion Bacillus cereus Cr4-1 presents good efficiency in bioreduction of hexavalent chromium and could be used in practical application.