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Bioreduction of hexavalent chromium flow-through column experiments and reactive transport modeling /

by 1970- Alam, Md Mahbub

Abstract (Summary)
by Md Mahbub Alam, Ph.D. Washington State University August 2004 Chair: David R. Yonge Bioreduction of Cr(VI) is considered a novel remediation alternative for Cr(VI) contaminated soil and groundwater. Many bacterial species can use Cr(VI) as an electron acceptor and reduce soluble and toxic Cr(VI) compounds to less soluble and less toxic Cr(III) compounds. Laboratory scale column experiments were performed to investigate Cr(VI) reduction by Shewanella oneidensis MR-1 in a continuous flow system. The column was packed with silica sand inoculated with S. oneidensis MR-1 as slurry in a laminar flow hood maintaining aseptic conditions. The feed solution was composed of simulated groundwater media (SGM) - lactate as the electron donor, and fumarate as the limiting electron acceptor. Following an initial growth period, Cr(VI) in the form of chromate was added to the feed. The feed and the effluent from the column were monitored for Cr(VI), total Cr, lactate, acetate, fumarate and succinate. Results of iv several experimental runs indicated that Cr(VI) in the effluent was below detection limit for several pore volumes, followed by Cr(VI) breakthrough for Cr(VI) feed concentrations equal to or greater than 1.94 mg/L. It is hypothesized that Cr(VI) breakthrough occurred due to Cr(VI) toxicity that inhibited bacterial growth. The Cr(VI) breakthrough corresponded with the breakthrough of fumarate, indicating microbial growth inhibition. A residual Cr(VI) reduction, ranging from 20% - 45% of the feed concentration, occurred after breakthrough, while no Cr(VI) or fumarate breakthrough was observed for feed Cr(VI) concentrations equal to or smaller than 1.32 mg/L. Therefore, long term biological reduction of Cr(VI) was dependent on the feed Cr(VI) concentration. Further, some soluble forms of Cr(III) complexes that may have been microbially produced were found in the column effluent. The column data, together with the batch kinetic information, was used to calibrate a mathematical model that describes reaction and transport of Cr(VI) in a column environment. The model was developed using RT3D, Reactive Transport in 3 Dimensions, with Cr(VI) biotransformation kinetics based on a recently developed dual enzyme Cr(VI) reduction kinetic model. The calibrated model was able to predict fate and transport of Cr(VI) in our laboratory scale sand columns. The model may be very useful for engineering design of in situ bioremediation. v
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School:Washington State University

School Location:USA - Washington

Source Type:Master's Thesis

Keywords:chromium soil remediation groundwater bioremediation

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