Kinetics of bioreduction of hexavalent chromium by poly vinyl alcohol-alginate immobilized cells of Ochrobactrum sp. Cr-B4 and comparison with free cells

Abstract

The cells of Ochrobactrum sp. Cr-B4 immobilized in PVA-alginate blended matrix could be successfully used for bioreduction of Cr(VI) from contaminated water. The removal mechanism included adsorption on solid-liquid interface and enzyme catalyzed chromate reduction. At lower concentrations the initial rate of Cr(VI) reduction with immobilized cells was found to be slightly higher than that of free cells owing to adsorption on the immobilization matrix. But after a certain time the rate of Cr(VI) reduction by free and immobilized cells was similar. The estimation of effectiveness factor (η), indicated that there were no diffusional limitations offered by the immobilization of Cr-B4 as the value of η was fond to be near “one” at different concentrations of Cr(VI). The kinetic analysis showed that both free and immobilized cells followed Michaelis–Menten kinetics with K_m and V_max of 456.1 mg/L and 14.67 mg/L/h for free cells respectively; 499.4 mg/L and 15.32 mg/L/h for immobilized cells respectively. The kinetic characteristics of Cr(VI) reduction were not altered by immobilization. This study reveals the potential applications of immobilized Cr-B4 in development of industrially feasible and economically viable bioremediation strategy for discharging Cr(VI) free effluent into the environment.

Keywords:

• Cr(VI)
• Ochrobactrum sp. Cr-B4
• Immobilization
• Effectiveness factor
• Michaelis–Menten kinetics