title: In situ bioreduction of uranium (VI) to submicromolar levels and reoxidation by dissolved oxygen.
abstract: 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.
authors.affiliation: Department of Civil and Environmental Engineering, Stanford University, Stanford, California 94305, USA.
authors.forename: Wei-Min
authors.initials: WM
authors.lastname: Wu
authors.forename: Jack
authors.initials: J
authors.lastname: Carley
authors.forename: Jian
authors.initials: J
authors.lastname: Luo
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Ginder-Vogel
authors.forename: Erick
authors.initials: E
authors.lastname: Cardenas
authors.forename: Mary Beth
authors.initials: MB
authors.lastname: Leigh
authors.forename: Chiachi
authors.initials: C
authors.lastname: Hwang
authors.forename: Shelly D
authors.initials: SD
authors.lastname: Kelly
authors.forename: Chuanmin
authors.initials: C
authors.lastname: Ruan
authors.forename: Liyou
authors.initials: L
authors.lastname: Wu
authors.forename: Joy
authors.initials: J
authors.lastname: Van Nostrand
authors.forename: Terry
authors.initials: T
authors.lastname: Gentry
authors.forename: Kenneth
authors.initials: K
authors.lastname: Lowe
authors.forename: Tonia
authors.initials: T
authors.lastname: Mehlhorn
authors.forename: Sue
authors.initials: S
authors.lastname: Carroll
authors.forename: Wensui
authors.initials: W
authors.lastname: Luo
authors.forename: Matthew W
authors.initials: MW
authors.lastname: Fields
authors.forename: Baohua
authors.initials: B
authors.lastname: Gu
authors.forename: David
authors.initials: D
authors.lastname: Watson
authors.forename: Kenneth M
authors.initials: KM
authors.lastname: Kemner
authors.forename: Terence
authors.initials: T
authors.lastname: Marsh
authors.forename: James
authors.initials: J
authors.lastname: Tiedje
authors.forename: Jizhong
authors.initials: J
authors.lastname: Zhou
authors.forename: Scott
authors.initials: S
authors.lastname: Fendorf
authors.forename: Peter K
authors.initials: PK
authors.lastname: Kitanidis
authors.forename: Philip M
authors.initials: PM
authors.lastname: Jardine
authors.forename: Craig S
authors.initials: CS
authors.lastname: Criddle
mesh_terms: D001419:Bacteria / Q000378:metabolism; D001673:Biodegradation, Environmental; D000431:Ethanol; D005618:Fresh Water / Q000737:chemistry; D019015:Geologic Sediments / Q000737:chemistry; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D012987:Soil; D012995:Solubility; D013057:Spectrum Analysis; D014481:United States; D014484:United States Environmental Protection Agency; D014501:Uranium / Q000302:isolation & purification* / Q000378:metabolism; D014875:Water Pollutants, Radioactive / Q000302:isolation & purification / Q000378:metabolism
chemical_list: D012987:Soil; D014875:Water Pollutants, Radioactive; D000431:Ethanol; D014501:Uranium; D010100:Oxygen