Grantee Research Project Results
2000 Progress Report: Improving the Performance of Permeable Reactive Barriers: Enhancing Reactivity and Longevity through Understanding of Surface Oxides
EPA Grant Number: R827117Title: Improving the Performance of Permeable Reactive Barriers: Enhancing Reactivity and Longevity through Understanding of Surface Oxides
Investigators: Tratnyek, Paul G. , Westall, John C.
Institution: Oregon Graduate Institute of Science & Technology , Oregon State University
EPA Project Officer: Aja, Hayley
Project Period: October 1, 1998 through September 30, 2001 (Extended to November 30, 2002)
Project Period Covered by this Report: October 1, 1999 through September 30, 2000
Project Amount: $374,252
RFA: Exploratory Research - Environmental Engineering (1998) RFA Text | Recipients Lists
Research Category: Safer Chemicals , Land and Waste Management , Sustainable and Healthy Communities
Objective:
Recent work on the remediation of contaminants with permeable reactive barriers (PRBs) containing zero-valent iron (ZVI) has shown that remediation performance is strongly affected by the layers of precipitates that form on the iron surface over time. The goal of this study is to explore the extent to which long-term performance of PRBs can be predicted and enhanced through a mechanistic understanding of the role of precipitates in the treatment zone. The approach includes electrochemical experiments with oxide film electrodes, column and batch experiments that combine solution phase chemistry with surface analysis, and modeling to integrate experimental results with theory.
Progress Summary:
The major developments during Year 2 were along four fronts: (1) at Oregon State Univerity (OSU), we studied the reduction of several contaminants on iron oxide electrodes; (2) at Oregon Graduate Institute (OGI), batch experiments have been performed that show the variation of reactivity with the composition of iron metal; (3) at OGI, we are doing column studies using TNT to probe how spatial and temporal changes in the geochemistry of the column influence its ability to remove contaminants; and (4) collectively, we have begun to develop a theoretical model of oxide film growth and how it effects contaminant reduction.
The first area of progress involved development and application of an electrochemical cell to study the rates of reduction of carbon tetrachloride (CT) and nitrobenzene (NB) by Fe(II) sites in a Fe(III)-oxide film. Fe(III) oxide films were prepared on gold electrodes, and the Fe(II) sites were introduced into the film by controlled electrochemical reduction of a small fraction of the Fe(III) in the film. The fundamental mechanism of reduction and the factors affecting the overall reduction rate were investigated by varying the Fe(II) content in the iron-oxide, controlling the mass transport of chemicals to the oxide surface, and varying the thickness of the oxide coating. The work constituted the doctoral thesis of Brian Logue, and will be published in a paper that is currently in preparation for Environmental Science and Technology [1,7].
The second area of progress revolves around batch experiments that are being performed with granular iron from a variety of sources and with model contaminants of various chemical types (including several colorimetric indicators as well as CT, NB, and trichloroethene). The granular iron also is being analyzed using a variety of surface analysis techniques (e.g., x-ray photoelectron spectroscopy). The results of these analyses are being correlated to obtain a better understanding of the factors that control the reactivity of aqueous contaminants with iron metal. Part of these results should be submitted shortly [5], and several more publications are expected.
The third area of progress, involving columns studies, has yielded two notable results: first, that TNT and its degradation products appear to be completely removed in columns packed with 100 percent granular iron, and second, that this appears to result from "geochemical" characteristics that develop in the columns but not batch systems. Both of these observations will be investigated further, and one publication from this has already taking shape [6]. Details on the fourth area of progress will be included in the final report.
Future Activities:
The electrochemical experiments will be extended to oxide-coated particles of iron metal. The column studies will be continued and extended to include more monitoring of geochemical properties like Eh and pH. The column design process will be integrated with the model development process.
Journal Articles on this Report : 5 Displayed | Download in RIS Format
| Other project views: | All 30 publications | 13 publications in selected types | All 11 journal articles |
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Agrawal A, Ferguson WJ, Gardner BO, Christ JA, Bandstra JZ, Tratnyek PG. Effects of carbonate species on the kinetics of dechlorination of 1,1,1-trichloroethane by zero-valent iron. Environmental Science & Technology 2002;36(20):4326-4333. |
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Logue BA, Westall JC. Kinetics of reduction of nitrobenzene and carbon tetrachloride at an iron-oxide coated gold electrode. Environmental Science & Technology 2003;37(11):2356-2362. |
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Miehr R, Tratnyek PG, Bandstra JZ, Scherer MM, Alowitz MJ, Bylaska EJ. Diversity of contaminant reduction reactions by zerovalent iron: role of the reductate. Environmental Science & Technology 2004;38(1):139-147. |
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Scherer MM, Johnson KM, Westall JC, Tratnyek PG. Mass transport effects on the kinetics of nitrobenzene reduction by iron metal. Environmental Science & Technology 2001;35(13):2804-2811. |
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Tratnyek PG, Reilkoff TE, Lemon AW, Scherer MM, Balko BA, Feik LM, Henegar BD. Visualizing redox chemistry: probing environmental oxidation-reduction reactions with indicator dyes. The Chemical Educator 2001;6(3):172-179. |
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Supplemental Keywords:
groundwater, treatment walls, passive technologies, iron metal., Air, Scientific Discipline, Waste, Remediation, Engineering, Environmental Chemistry, Engineering, Chemistry, & Physics, Groundwater remediation, surface oxidation, groundwater contamination, adsorbents, kinetic models, permeable reaction barriers, electrochemical technology, chlorinated solvents, ironRelevant Websites:
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.