Effects of organic carbon supply rates on mobility of previously bioreduced uranium in a contaminated sediment

Journal Article · Thu May 15 04:00:00 EDT 2008 · Environmental Science and Technology

DOI:https://doi.org/10.1021/es800951h· OSTI ID:940401

Wan, J; Tokunaga, T K; Kim, Y; Brodie, E; Daly, R; Hazen, T C; Firestone, M K

Bioreduction-based strategies for remediating uranium (U)-contaminated sediments face the challenge of maintaining the reduced status of U for long times. Because groundwater influxes continuously bring in oxidizing terminal electron acceptors (O{sub 2}, NO{sub 3}{sup -}), it is necessary to continue supplying organic carbon (OC) to maintain the reducing environment after U bioreduction is achieved. We tested the influence of OC supply rates on mobility of previously microbial reduced uranium U(IV) in contaminated sediments. We found that high degrees of U mobilization occurred when OC supply rates were high, and when the sediment still contained abundant Fe(III). Although 900 days with low levels of OC supply minimized U mobilization, the sediment redox potential increased with time as did extractable U(VI) fractions. Molecular analyses of total microbial activity demonstrated a positive correlation with OC supply and analyses of Geobacteraceae activity (RT-qPCR of 16S rRNA) indicated continued activity even when the effluent Fe(II) became undetectable. These data support our earlier hypothesis on the mechanism responsible for re-oxidation of microbial reduced U(IV) under reducing conditions; that microbial respiration caused increased (bi)carbonate concentrations and formation of stable uranyl carbonate complexes, thereby shifted U(IV)/U(VI) equilibrium to more reducing potentials. The data also suggested that low OC concentrations could not sustain the reducing condition of the sediment for much longer time.

• Research Organization: Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (US)
• Sponsoring Organization: Earth Sciences Division
• DOE Contract Number: AC02-05CH11231
• OSTI ID: 940401
• Report Number(s): LBNL-619E
• Journal Information: Environmental Science and Technology, Journal Name: Environmental Science and Technology; ISSN ESTHAG; ISSN 0013-936X
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
AVAILABILITY
BINDING ENERGY
CARBON
ELECTRONS
HYPOTHESIS
REDOX POTENTIAL
RESPIRATION
SEDIMENTS
URANIUM
URANYL CARBONATES
VALENCE