title: Uranium immobilization by sulfate-reducing biofilms.
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 microM. 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.
authors.affiliation: Center for Biofilm Engineering and Department of Civil Engineering, Montana State University, Bozeman, Montana 59717-3980, USA.
authors.forename: Haluk
authors.initials: H
authors.lastname: Beyenal
authors.forename: Rajesh K
authors.initials: RK
authors.lastname: Sani
authors.forename: Brent M
authors.initials: BM
authors.lastname: Peyton
authors.forename: Alice C
authors.initials: AC
authors.lastname: Dohnalkova
authors.forename: James E
authors.initials: JE
authors.lastname: Amonette
authors.forename: Zbigniew
authors.initials: Z
authors.lastname: Lewandowski
mesh_terms: D018441:Biofilms; D011232:Chemical Precipitation; D006862:Hydrogen Sulfide / Q000032:analysis; D012995:Solubility; D013431:Sulfates / Q000378:metabolism; D016999:Sulfur-Reducing Bacteria / Q000502:physiology*; D014501:Uranium / Q000737:chemistry / Q000302:isolation & purification*; D014875:Water Pollutants, Radioactive / Q000302:isolation & purification*
chemical_list: D013431:Sulfates; D014875:Water Pollutants, Radioactive; D014501:Uranium; D006862:Hydrogen Sulfide