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Title: Mesoscale Biotransformation of Uranium: Influences of Organic Carbon Supply Rates and Sediment Oxides

Abstract

Remediation and long-term stewardship of uranium-contaminated sediments and groundwaters are critical problems at a number of DOE facilities and mining sites. Some remediation strategies based on in-situ bioreduction of U are potentially effective in significantly decreasing U concentrations in groundwaters. However, a number of basic processes require understanding in order to identify conditions more conducive to success of reduction-based U stabilization. Our current research targets several of these issues including: (1) effects of organic carbon (OC) forms and supply rates on stability of bioreduced U, (2) the roles of Fe(III)- and Mn(III,IV)-oxides as potential U oxidants in sediments, and (3) microbial community changes in relation to U redox changes. These issues were identified in our previous study on U bioreduction and reoxidation (Wan et al., 2005). Most of our studies are being conducted on historically U-contaminated sediments from Area 2 of the Field Research Center, Oak Ridge National Laboratory, in flow-through columns simulating in-situ field remediation.

Authors:
; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
926149
Report Number(s):
CONF/ERSP2007-1024940a
R&D Project: ERSD 1024940a; TRN: US0802450
Resource Type:
Conference
Resource Relation:
Conference: Annual Environmental Remediation Science Program (ERSP) Principal Investigator Meeting, April 16-19, 2007, Lansdowne, VA
Country of Publication:
United States
Language:
English
Subject:
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; 54 ENVIRONMENTAL SCIENCES; BIOREMEDIATION; URANIUM; SEDIMENTS; GROUND WATER; ORGANIC COMPOUNDS; IRON OXIDES; MANGANESE OXIDES; OXIDIZERS; MICROORGANISMS; REDOX REACTIONS; ORNL; FIELD TESTS

Citation Formats

Tetsu Tokunaga, Jiamin Wan, Yongman Kim, Rebecca Daly, Eoin Brodie, Mary Firestone, Terry Hazen, Steve Sutton, Matt Newville, Tony Lanzirotti, and Bill Rao. Mesoscale Biotransformation of Uranium: Influences of Organic Carbon Supply Rates and Sediment Oxides. United States: N. p., 2007. Web.
Tetsu Tokunaga, Jiamin Wan, Yongman Kim, Rebecca Daly, Eoin Brodie, Mary Firestone, Terry Hazen, Steve Sutton, Matt Newville, Tony Lanzirotti, & Bill Rao. Mesoscale Biotransformation of Uranium: Influences of Organic Carbon Supply Rates and Sediment Oxides. United States.
Tetsu Tokunaga, Jiamin Wan, Yongman Kim, Rebecca Daly, Eoin Brodie, Mary Firestone, Terry Hazen, Steve Sutton, Matt Newville, Tony Lanzirotti, and Bill Rao. Thu . "Mesoscale Biotransformation of Uranium: Influences of Organic Carbon Supply Rates and Sediment Oxides". United States. doi:. https://www.osti.gov/servlets/purl/926149.
@article{osti_926149,
title = {Mesoscale Biotransformation of Uranium: Influences of Organic Carbon Supply Rates and Sediment Oxides},
author = {Tetsu Tokunaga and Jiamin Wan and Yongman Kim and Rebecca Daly and Eoin Brodie and Mary Firestone and Terry Hazen and Steve Sutton and Matt Newville and Tony Lanzirotti and Bill Rao},
abstractNote = {Remediation and long-term stewardship of uranium-contaminated sediments and groundwaters are critical problems at a number of DOE facilities and mining sites. Some remediation strategies based on in-situ bioreduction of U are potentially effective in significantly decreasing U concentrations in groundwaters. However, a number of basic processes require understanding in order to identify conditions more conducive to success of reduction-based U stabilization. Our current research targets several of these issues including: (1) effects of organic carbon (OC) forms and supply rates on stability of bioreduced U, (2) the roles of Fe(III)- and Mn(III,IV)-oxides as potential U oxidants in sediments, and (3) microbial community changes in relation to U redox changes. These issues were identified in our previous study on U bioreduction and reoxidation (Wan et al., 2005). Most of our studies are being conducted on historically U-contaminated sediments from Area 2 of the Field Research Center, Oak Ridge National Laboratory, in flow-through columns simulating in-situ field remediation.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Apr 19 00:00:00 EDT 2007},
month = {Thu Apr 19 00:00:00 EDT 2007}
}

Conference:
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  • Remediation of uranium (U) contaminated sediments through in-situ stimulation of bioreduction to insoluble UO{sub 2} is a potential treatment strategy under active investigation. Previously, we found that newly reduced U(IV) can be reoxidized under reducing conditions sustained by a continuous supply of organic carbon (OC) because of residual reactive Fe(III) and enhanced U(VI) solubility through complexation with carbonate generated through OC oxidation. That finding motivated this investigation directed at identifying a range of OC supply rates that is optimal for establishing U bioreduction and immobilization in initially oxidizing sediments. The effects of OC supply rate, from 0 to 580 mmolmore » OC (kg sediment){sup -1} year{sup -1}, and OC form (lactate and acetate) on U bioreduction were tested in flow-through columns containing U-contaminated sediments. An intermediate supply rate on the order of 150 mmol OC (kg sediment){sup -1} year{sup -1} was determined to be most effective at immobilizing U. At lower OC supply rates, U bioreduction was not achieved, and U(VI) solubility was enhanced by complexation with carbonate (from OC oxidation). At the highest OC supply rate, resulting highly carbonate-enriched solutions also supported elevated levels of U(VI), even though strongly reducing conditions were established. Lactate and acetate were found to have very similar geochemical impacts on effluent U concentrations (and other measured chemical species), when compared at equivalent OC supply rates. While the catalysts of U(VI) reduction to U(IV) are presumably bacteria, the composition of the bacterial community, the Fe reducing community, and the sulfate reducing community had no direct relationship with effluent U concentrations. The OC supply rate has competing effects of driving reduction of U(VI) to low solubility U(IV) solids, as well as causing formation of highly soluble U(VI)-carbonato complexes. These offsetting influences will require careful control of OC supply rates in order to optimize bioreduction-based U stabilization.« less
  • 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 withmore » 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.« less
  • The extent of reductive dechlorination taking place in contaminated, estuarine sediments was investigated. Specifically, the effect of contaminant and organic matter bioavailability on the reductive dechlorination of the sediment-bound chlorobenzenes was the main focus of the work presented here. Sediment and water samples were collected from a contaminated estuarine system. Hexachlorobenzene and other chlorinated benzene congeners were found to be the predominant chlorinated compounds. Anaerobic batch assays revealed that the sediment natural organic matter is recalcitrant and unable to support active microbial growth. Sediment nutrients (e.g., N.P.) were available in sufficient quantities to support an accelerated microbial growth. Static microcosmsmore » were constructed with sediment and water from the study site. The sediment microbial consortia were able to reductively dechlorinate the sediment-bound polychlorinated benzene congeners primarily to dichlorobenzene isomers. However, the extent of hexachlorobenzene removal over a long incubation time (more than 480 d) was only 43% and most of it occurred during the first 200 d of incubation. Both the recalcitrant nature of the sediment organic matter and the strong partitioning of the chlorinated compounds were responsible for the low extent of contaminant transformation. Addition of a degradable organic compound increased the extent of contaminant reductive dechlorination.« less