Comparative Kinetics of Bacterial Reduction of Chromium

Most previous studies of bacterial reduction of chromium have been done with pure cultures that are not likely to be found in ground water, and at hexavalent chromium concentrations much greater than typically present in contaminated ground water. Further, most previous work has been performed with complex laboratory substrates that would not be suitable for in situ application. In this study, mixed cultures were enriched from three diverse soil sources: surface soil, subsurface soil, and river sediment. The enrichment medium contained 10 mg Cr⁶⁺/L and sucrose as the carbon source. The three mixed cultures obtained from the diverse soil samples were transferred to batch reactors and exhibited similar chromium reduction enzyme kinetics at stationary phase. The maximum specific reduction rates were between 0.98 and 3.3 mg Cr⁶⁺/(g dry cells$\dot{s}$h) and the half velocity constants were between 0.39 and 1.48 mg Cr⁶⁺/L. The relatively narrow range of values for kinetic parameters suggests that a conservative engineering design for in situ remediation could be applied over a wide range of contaminated sites at the Cr(VI) concentrations examined.