Pilot-Scale in Situ Bioremediation of Uranium in a Highly Contaminated Aquifer. 1. Conditioning of a Treatment Zone
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- 作者：Wei-Min Wu ; Jack Carley ; Michael Fienen ; Tonia Mehlhorn ; Kenneth Lowe ; Jennifer Nyman ; Jian Luo ; Margaret E. Gentile ; Raj Rajan ; Daniel Wagner ; Robert F. Hickey ; Baohua Gu ; David Watson ; Olaf A. Cirpk
- 刊名：Environmental Science & Technology
- 出版年：2006
- 出版时间：June 15, 2006
- 年：2006
- 卷：40
- 期：12
- 页码：3978 - 3985
- 全文大小：461K
- 年卷期：v.40,no.12(June 15, 2006)
- ISSN：1520-5851
文摘
To evaluate the potential for in situ bioremediation ofU(VI) to sparingly soluble U(IV), we constructed a pilottest facility at Area 3 of the U.S. Department of EnergyNatural and Accelerated Bioremediation Research (NABIR)Field Research Center (FRC) in Oak Ridge, TN. Thefacility is adjacent to the former S-3 Ponds which receivedtrillions of liters of acidic plating wastes. High levels ofuranium are present, with up to 800 mg kg-1 in the soil and84-210 
M in the groundwater. Ambient groundwaterhas a highly buffered pH of ~3.4 and high levels of aluminum(12-13 mM), calcium (22-25 mM), and nitrate (80-160mM). Adjusting the pH of groundwater to ~5 within theaquifer would deposit extensive aluminum hydroxideprecipitate. Calcium is present in the groundwater at levelsthat inhibit U(VI) reduction, but its removal by injectionof a high pH solution would generate clogging precipitate.Nitrate also inhibits U(VI) reduction and is present atsuch high concentrations that its removal by in situdenitrification would generate large amounts of N2 gasand biomass. To establish and maintain hydraulic control,we installed a four well recirculation system parallel togeologic strike, with an inner loop nested within an outerloop. For monitoring, we drilled three boreholes perpendicular to strike across the inner loop and installed multilevelsampling tubes within them. A tracer pulse with cleanwater established travel times and connectivity betweenwells and enabled the assessment of contaminant releasefrom the soil matrix. Subsequently, a highly conductiveregion of the subsurface was prepared for biostimulationby removing clogging agents and inhibitors and increasingpH. For 2 months, groundwater was pumped from thehydraulically conductive zone; treated to remove aluminum,calcium, and nitrate, and supplemented with tap water;adjusted to pH 4.3-4.5; then returned to the hydraulicallyconductive zone. This protocol removed most of theaqueous aluminum and calcium. The pH of the injectedtreated water was then increased to 6.0-6.3. With additionalflushing, the pH of the extracted water gradually increasedto 5.5-6.0, and nitrate concentrations fell to 0.5-1.0mM. These conditions were judged suitable for biostimulation.In a companion paper (Wu et al., Environ. Sci. Technol.2006, 40, 3978-3987), we describe the effects of ethanoladdition on in situ denitrification and U(VI) reductionand immobilization.
M in the groundwater. Ambient groundwaterhas a highly buffered pH of ~3.4 and high levels of aluminum(12-13 mM), calcium (22-25 mM), and nitrate (80-160mM). Adjusting the pH of groundwater to ~5 within theaquifer would deposit extensive aluminum hydroxideprecipitate. Calcium is present in the groundwater at levelsthat inhibit U(VI) reduction, but its removal by injectionof a high pH solution would generate clogging precipitate.Nitrate also inhibits U(VI) reduction and is present atsuch high concentrations that its removal by in situdenitrification would generate large amounts of N2 gasand biomass. To establish and maintain hydraulic control,we installed a four well recirculation system parallel togeologic strike, with an inner loop nested within an outerloop. For monitoring, we drilled three boreholes perpendicular to strike across the inner loop and installed multilevelsampling tubes within them. A tracer pulse with cleanwater established travel times and connectivity betweenwells and enabled the assessment of contaminant releasefrom the soil matrix. Subsequently, a highly conductiveregion of the subsurface was prepared for biostimulationby removing clogging agents and inhibitors and increasingpH. For 2 months, groundwater was pumped from thehydraulically conductive zone; treated to remove aluminum,calcium, and nitrate, and supplemented with tap water;adjusted to pH 4.3-4.5; then returned to the hydraulicallyconductive zone. This protocol removed most of theaqueous aluminum and calcium. The pH of the injectedtreated water was then increased to 6.0-6.3. With additionalflushing, the pH of the extracted water gradually increasedto 5.5-6.0, and nitrate concentrations fell to 0.5-1.0mM. These conditions were judged suitable for biostimulation.In a companion paper (Wu et al., Environ. Sci. Technol.2006, 40, 3978-3987), we describe the effects of ethanoladdition on in situ denitrification and U(VI) reductionand immobilization.