Biological Cr(VI) immobilisation in saturated aquifer zone using culture inoculated soil columns.

Remediation of Cr(VI) requires the reduction of the mobile state [Cr(VI)], which exists in the natural environment as the oxyanionic species (CrxOy(z)(-)), to the less mobile trivalent state [Cr(III)], which readily forms the hydroxide precipitate [Cr(OH)3(s)] under natural pH conditions. In this study, Cr(VI) reduction is investigated using inoculated microcosm aquifer systems operated as fully submerged plug flow systems. The system was design to simulate the operation of a microbial contaminant barrier in the saturated zone of an open aquifer system. No organic carbon sources and no air was introduced to simulate Cr(VI) reduction under oxygen free conditions. The inoculated microcosm column operated at influent feed concentrations of 10, 20, and 40 mg/L, and a hydraulic retention time of 12 hours achieved complete removal of Cr(VI) over a 90 cm distance. Steady-state conditions were obtained in less than 48 hours under feed concentrations of 10 and 20 mg/L. Very little Cr(VI) reduction was observed in non-inoculated microcosm controls operated under identical conditions.