In situ bioreduction of uranium (VI) in situ and stability of immobilized uranium: Impact of dissolved oxygen
Date
2007-08Author
Wu, Wei-Min
Carley, Jack
Luo, Jian
Ginder-Vogel, Matthew A.
Cardenas, Erick
Leigh, Mary Beth
Hwang, Chiachi
Kelly, Shelly D.
Ruan, Chuanmin
Wu, Liyou
Nostrand, Joy V.
Gentry, Terry J.
Lowe, K. A.
Mehlhorn, T. L.
Carroll, Sue L.
Luo, Wensui
Gu, Baohua
Watson, David B.
Kemner, K. M.
Marsh, Terence
Tiedje, J. M.
Zhou, Jizhong
Fendorf, Scott
Kitanidis, Peter K.
Jardine, Phil M.
Criddle, Craig S.
Metadata
Show full item recordAbstract
Groundwater within Area 3 of the U.S. Department of Energy (DOE) Environmental Remediation Sciences Program (ERSP) Field Research Center at Oak Ridge, TN (ORFRC) contains up to 135 microM uranium as U(VI). Through a series of experiments at a pilot scale test facility, we explored the lower limits of groundwater U(VI) that can be achieved by in-situ biostimulation and the effects of dissolved oxygen on immobilized uranium. Weekly 2-day additions of ethanol over a 2-year period stimulated growth of denitrifying, Fe(III)-reducing, and sulfate-reducing bacteria, and immobilization of uranium as U(IV), with dissolved uranium concentrations decreasing to low levels. Following sulfite addition to remove dissolved oxygen, aqueous U(VI) concentrations fell below the U.S. Environmental Protection Agengy maximum contaminant limit (MCL) for drinking water (< 30/microg L(-1) or 0.126 microM). Under anaerobic conditions, these low concentrations were stable, even in the absence of added ethanol. However, when sulfite additions stopped, and dissolved oxygen (4.0-5.5 mg L(-1)) entered the injection well, spatially variable changes in aqueous U(VI) occurred over a 60 day period, with concentrations increasing rapidly from < 0.13 to 2.0 microM at a multilevel sampling (MLS) well located close to the injection well, but changing little at an MLS well located further away. Resumption of ethanol addition restored reduction of Fe(III), sulfate, and U(VI) within 36 h. After 2 years of ethanol addition, X-ray absorption near-edge structure spectroscopy (XANES) analyses indicated that U(IV) comprised 60-80% of the total uranium in sediment samples. Atthe completion of the project (day 1260), U concentrations in MLS wells were less than 0.1 microM. The microbial community at MLS wells with low U(VI) contained bacteria that are known to reduce uranium, including Desulfovibrio spp. and Geobacter spp., in both sediment and groundwater. The dominant Fe(III)-reducing species were Geothrix spp.
Citation
Wu, WM, Carley J, Luo J, Ginder-Vogel MA, Cardenas E, Leigh MB, Hwang C, Kelly SD, Ruan C, Wu L, Van Nostrand J, Gentry T, Lowe K, Mehlhorn T, Carroll S, Luo W, Fields MW, et al, "In situ bioreduction of uranium (VI) in situ and stability of immobilized uranium: Impact of dissolved oxygen," Environ Sci Technol, 2007 41(16):5716-5723