Research and Demonstration Using Zero Valent Iron in
Permeable Barriers for Groundwater Contaminant Removal
ESD researchers have considerable experience regarding research and development on the use of permeable reactive barriers for remediation of contaminated groundwater. Beginning in 1994 both laboratory bench- and pilot-scale studies has been conducted on the mechanisms and kinetics of contaminant degradation/ transformation, including organics (e.g., perchloroethylene, trichloroethylene or TCE, polychlorinated biphenyl, and carbon tetrachloride) and inorganics (e.g., Tc, U, NO3-), using zero-valence iron. These activities resulted in large-scale demonstrations and new efforts to understand field performance issues.
Early laboratory research on TCE degradation at ORNL led to the first reported observation of degradation byproducts, including vinyl chloride (VC). In order to enhance dechlorination reaction rates and minimize byproduct formation, bi-metal systems of palladized iron were developed (and patented). Pilot-scale demonstrations have shown that hydrogen gas production within the iron media can cause a stoppage of fluid flow. Additionally, biochemical reactions within the iron media generated a suite of inorganic precipitates and biomass, which reduced permeability, particularly at redox sensitive boundaries as well as throughout the media.
ESD researchers are involved in two separate installations of permeable reactive barriers (PRBs) at the DOE Y-12 Plant. A funnel and gate reactive barrier configuration was installed in one part of the contaminant plume (Pathway 1) in December 1997 and a permeable reactive trench, backfilled with gravel and iron (no impermeable barrier), was installed in another part of the plume (Pathway 2) in November 1997. Target contaminants in the plume include a mixture of U, Tc, chlorinated organic compounds, and NO3-. Zero valent iron filings are used for the removal of metal by redox-driven precipitation and sorption on iron (e.g., U and Tc). Chlorinated organics are rendered harmless through dechlorination. Results at Pathway 2 show that the iron is effectively removing U, NO3-, and Tc as anticipated from results of previous laboratory studies. After ~ 1.5 years of operation, cores of the iron media recovered from this barrier show varying degrees of corrosion and mineral precipitation, including iron sulfide (catalyzed by sulfate-reducing bacteria), calcium carbonate (aragonite), siderite (iron carbonate), and iron oxyhydroxides (goethite, akagneite, and amorphous phases). Uranium was measured at concentrations as high as 144 mg/kg in the iron and was concentrated near the iron/soil interface, suggesting that rapid removal had occurred. Microbial activity in groundwater and soils was elevated in the trench and iron media relative to background conditions. Sulfate and iron reducing bacteria as well as denitrifiers were identified.
A three-year, tri-agency initiative, including researchers from DOE, DoD, and EPA, began in FY1999 and is focusing on long-term barrier performance evaluation. The objective is to better understand the importance of hydraulic and geochemical factors in controlling groundwater flow paths through the iron, the potential for clogging, and long-term treatment effectiveness of contaminants. Current activities include: (1) evaluating the monitoring schemes at existing PRB sites owned by DOE, DoD, and EPA and selecting representative sites for more focused study; (2) investigating changes in contaminant removal efficiency, chemical precipitation and microbial build up that affects the life of the PRBs; and (3) evaluating hydraulic monitoring methods and key geochemical indicators. The results of these investigations will be used to recommend suitable site characterization and performance/longevity monitoring strategies and procedures.
References
Liang, L., N. E. Korte, B. Gu, R. Puls, and C. Reeter. Geochemical and microbial reactions affecting long-term performance of in situ iron barriers. Adv. In Environ. Research. (in press)
Gu, B., T.J. Phelps, L. Liang, M.J. Dickey, Y. Roh, B.L. Kinsall, A.V. Palumbo, and G.K. Jacobs. 1999. Biogeochemical dynamics in zero-valent iron columns: implications for permeable reactive barriers. Environ. Sci. Technol. 33:2170-2177.
Birke, V., L. Liang, and H. Burmeier. 1999. Durchströmte Reaktoren zur In-situ Grundwassersanierung. TerraTech 1999(1):23-25.
Gu, B., L. Liang, M. J. Dickey, X. Yin, and S. Dai. 1998. Reductive precipitation of uranium(VI) by zero-valence iron. Environ. Sci. Technol. 32:3366-3373.
Liang, L. and B. Gu, 1998. The treatment of groundwater with Mixed-Wastes: reductive dechlorination of TCE and reductive precipitation of uranium. NATO/ CCMS Pilot Study, EPA 542-R-9-003, May 1998. NATO publication No 229. pp. 36-43.
Gu, B., L. Liang, P. Cameron, O.R. West, and N. Korte. 1997. TCE and PCB degradation by zero-valence iron in the presence of surfactant. Proceedings of the 1997 International Containment Technology Conference and Exhibition, St. Petersburg, FL. pp. 760-766.
Korte, N., O.R. West, L. Liang, M.J. Pelfrey, and T.C. Houk, 1997. A field-scale test facility for permeable reactive barriers at the Portsmouth gaseous diffusion plant. Federal facilities environmental journal, Autumn, p. 105-114.
Korte, N.E., L. Liang, B. Gu, M.T. Muck, J.L. Zutman, R.M. Schlosser, R.L. Siegrist, T.C. Touk, and Q. Fernando. 1997. "In Situ Treatment of Mixed Contaminants In Groundwater: Application Of Zero-Valence Iron And Palladized Iron For Treatment Of Groundwater Contaminated With Trichlorethene And Technetium-99." ORNL-TM-13530, Oak Ridge, TN.
Liang, L., N.E. Korte, J.D. Goodlaxson, J. Clausen, Q. Fernando, and R. Muftikian. 1997. "Byproduct formation during the reduction of TCE by zero-valence iron and palladized iron." Ground Water Monitoring and Review, Winter: 122-127.
West, O.R., R.L. Siegrist, T.C. Houk, L. Liang, S.Y. Lee, A. Laase, D.A. Pickering, M.J. Dickey, X. Yin, and B. Gu. 1997. The X-625 Treatment Facility: Assessment of Reactive Barrier Technology at PORTS. POEF_LMES-174, Piketon, OH.
Liang, L., O.R. West, N.E. Korte, J.D. Goodlaxson, D.A. Pickering, J.L. Zutman, F.J. Anderson, C.A. Welch, M.J. Pelfrey, and M.J. Dickey. 1997. A field-scale test of trichloroethylene dechlorination using iron filings for the X-120/X749 groundwater plume. ORNL-TM-13410, Oak Ridge, TN.
Korte, N., L. Liang, R. Muftikian, C. Grittini, and Q. Fernando, 1997. "The dechlorination of hydrocarbons." Platinum Metals Review 41(1):2-6.
Liang, L., B. Gu, and X. Yin. 1996. "Removal of Technetium-99 from Contaminated Groundwater with Sorbents and Reductive Materials". Separations Technol. 6:111-122.
Liang, L. and J.D. Goodlaxson. 1995. "Kinetics and byproducts of reductive dechlorination of ground water TCE with zero-valence iron," Emerging technologies in hazardous waste management VII, extended abstract. pp. 46-49, American chemical Society, Atlanta, GA.
Liang, L., J.D. Goodlaxson, N.E. Korte, J.L. Clausen, and D.T. Davenport. 1995. ORNL/MMES Research into Remedial Applications of Zero-Valence Metals. 1: Laboratory analysis of reductive dechlorination of trichloroethene. 209th National Meeting, Anaheim, CA. American Chemical Society 35(1):728-731.
For more information, contact:
Baohua Gu (gub1@ornl.gov, 865-574-7286)
Revised: 5/14/01
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