Web Release Date: February 25,
Uranium Immobilization by Sulfate-Reducing Biofilms
and
Center for Biofilm Engineering and Department of Civil Engineering, Montana State University, Bozeman, Montana 59717-3980, Department of Chemical Engineering, Center for Multiphase Environmental Research, Washington State University, Dana Hall Room 118, Pullman, Washington 99164-2710, and Fundamental Science Directorate, Pacific Northwest National Laboratory, P.O. Box 999, K8-96, 3335 Q Avenue, Richland, Washington 99352
Received for review August 5, 2003
Revised manuscript received January 14, 2004
Accepted January 16, 2004
Abstract:
Hexavalent uranium [U(VI)] was immobilized using biofilms
of the sulfate-reducing bacterium (SRB) Desulfovibrio
desulfuricans G20. The biofilms were grown in flat-plate
continuous-flow reactors using lactate as the electron donor
and sulfate as the electron acceptor. U(VI) was continuously
fed into the reactor for 32 weeks at a concentration of
126 
M. During this time, the soluble U(VI) was removed
(between 88 and 96% of feed) from solution and immobilized
in the biofilms. The dynamics of U immobilization in the
sulfate-reducing biofilms were quantified by estimating: (1)
microbial activity in the SRB biofilm, defined as the
hydrogen sulfide (H2S) production rate and estimated
from the H2S concentration profiles measured using
microelectrodes across the biofilms; (2) concentration of
dissolved U in the solution; and (3) the mass of U precipitated
in the biofilm. Results suggest that U was immobilized in
the biofilms as a result of two processes: (1) enzymatically
and (2) chemically, by reacting with microbially generated
H2S. Visual inspection showed that the dissolved sulfide
species reacted with U(VI) to produce a black precipitate.
Synchrotron-based U L3-edge X-ray absorption near
edge structure (XANES) spectroscopy analysis of U
precipitated abiotically by sodium sulfide indicated that
U(VI) had been reduced to U(IV). Selected-area electron
diffraction pattern and crystallographic analysis of
transmission electron microscope lattice-fringe images
confirmed the structure of precipitated U as being that of
uraninite.
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