Microbiological reduction of hexavalent chromium by indigenous chromium-resistant bacteria in sand column experiments.

Indigenous bacteria that are resistant to high concentrations of Cr(VI) were isolated from a Cr-contaminated sediment. Sand column experiments were conducted using the isolated bacteria to investigate microbial effects on Cr(VI) reduction in open systems that simulated subsurface conditions. The indigenous Cr-resistant bacteria appeared to reduce Cr(VI) in the column experiments. When 12 mg/L of Cr(VI) was injected into the columns, the removal efficiencies of Cr(VI) by the isolated bacteria were 39.1%, 62.5%, and 63.6% at 24, 48, and 72 h retention times of Cr(VI) solution, respectively. These results imply that the linear velocity of groundwater or pore water should be less than 0.63 cm/h for effective removal of Cr(VI) in subsurface conditions. In comparison, the noninoculated control column did not show a significant variation in dissolved Cr(VI) concentration. The results indicated that reduction of Cr(VI) was occurring in the column due to the activity of the indigenous bacteria.