Grantee Research Project Results
1998 Progress Report: Assessment of Biotic and Abiotic Processes Controlling the Fate of Chlorinated Solvents in Mixed-Waste Under Iron- and Sulfate-Reducing Conditions Using Laboratory and In Situ Microcosms
EPA Grant Number: R825958Title: Assessment of Biotic and Abiotic Processes Controlling the Fate of Chlorinated Solvents in Mixed-Waste Under Iron- and Sulfate-Reducing Conditions Using Laboratory and In Situ Microcosms
Investigators: Hayes, Kim F. , Adriaens, Peter , Barcelona, Michael J.
Institution: University of Michigan
EPA Project Officer: Aja, Hayley
Project Period: November 17, 1997 through November 16, 2000
Project Period Covered by this Report: November 17, 1997 through November 16, 1998
Project Amount: $449,975
RFA: EPA/DOE/NSF/ONR - Joint Program On Bioremediation (1997) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management
Objective:
The major objective of this research is to evaluate the relative importance of biotic and abiotic reductive dechlorination processes under iron- and sulfate-reducing conditions in both simple and mixed-waste systems.Progress Summary:
In this project period, we performed abiotic reductive dechlorination using synthetic Fe(II) solids as well as purely biological studies aimed at quantifying reductive dechlorination in the absence of solids under sulfate and iron reducing conditions. A comparison of rates and reaction products provides one means by which biotic and abiotic transformation might be distinguished. We obtained a quantitative description of the kinetics of the abiotic transformation of trichloroethylene (TCE) and tetrachloroethylene (PCE) by FeS. Rates of hexachloroethane (HCA) reductive dechlorination were also measured in the presence of the iron (II) bearing minerals: biotite, hornblende, siderite and magnetite. In our biological studies, the kinetics of cell mediated carbon tetrachloride (CT) dechlorination were characterized for the iron reducing bacteria Geobacter metallireducens. A sulfate reducing bacteria was also cultured and is currently being used to generate FeS for reductive dechlorination in sulfidogenic environments.
Figure 1. Aqueous concentrations of TCE,
acetylene, and cis-DCE versus time; 10 g/L FeS, pH 8.3. Data points are
experimentally-measured values and lines are model fits.
Accomplishments and Research Results:
Experiments were performed to determine the rates and products of transformation of TCE and PCE by FeS. The principal reaction product for TCE transformation by FeS was acetylene, while cis-1,2-dichloroethylene (cis-DCE) and vinyl chloride (VC) were minor products. Data were interpreted assuming parallel transformation of TCE to these two products, with VC most likely forming from slow hydrogenolysis of cis-DCE. The solution to the differential equations describing such a reaction scheme indicated that TCE was transformed to acetylene 11.8 ? 1.1 times faster than to cis-DCE. Solutions to the differential equations are plotted along with experimental data in Figure 1. Detection of acetylene as the principal TCE reductive dechlorination product contrasts with the sequential hydrogenolysis commonly observed in the transformation of TCE in microbiological systems, which can result in the accumulation of significant quantities of the harmful intermediates cis-DCE and VC. Similar results were obtained for the transformation of PCE by FeS.
Results were also obtained for HCA reduction by other iron (II) bearing aquifer solids expected to be present under iron reducing conditions but so far none have been reactive in the absence of added dissolved Fe2+. When reduced iron was added to solutions containing biotite, hornblende, and siderite, HCA was dechlorinated, but no degradation was observed in solutions containing magnetite. Hornblende (kobs 0.823/hr) was more reactive than biotite (kobs 0.269/hr) when rates were normalized to surface area. No surface area measurements are available for siderite. In absence of the Fe(II) solid phases, dissolved Fe(II) is unreactive. We are further investigating the basis for the activation of the reduced iron solids by the addition of Fe(II) and the apparent lack of reactivity of synthetic magnetite observed in these studies. Because our past work has demonstrated that biogenically produced magnetite is quite reactive, we hypothesize that the synthetically produced material may have become passivated with an oxic film, rendering it less reactive.
Biological experiments have been conducted using cell suspensions of the dissimilative iron reducing bacteria Geobacter metallireducens At carbon tetrachloride (CT) concentrations less than 100 µM, cell mediated dechlorination rates were found to follow first order kinetics (protein normalized first order rate constant = 0.14 ml/hr-mg-protein). The only volatile product detected was chloroform (CF) which accounted for approximately 27% of the transformed CT. No other products were detected and are presumed to be non-volatile or cell bound. Inhibition studies were also conducted to examine the effect of CT concentrations on iron reduction rates. Initial iron reduction rates appeared to be independent of CT concentrations, while over prolonged periods (>1 hr) the presence of CT resulted in diminished iron reducing activity (Figure 2). The initial rate data indicate that CT and Fe(III) are not reduced at the same electron transfer site within the organism although they do compete for common metabolic reductants (uncompetitive inhibition). The diminished iron reducing activity over prolonged periods may be due to toxicity of dechlorination products such as CF or CCl3? radicals.
Figure 2. Figure 2. Reductive dechlorination of CT at various temperatures in a culture of iron reducing bacteria containing Biogenic magnetite. Inset illustrates the Arrhenius plot for the reaction.
Extending the biological investigations to sulfidogenic environments, a sulfate-reducing bacterium, Desulfobacterium autotrophicum, has been obtained and cultured to conduct experiments that parallel the work with G. metallireducens. The culture has been successfully maintained in sulfate rich media amended with acetate or lactate.
Future Activities:
The influence of pH and ionic and organic solutes on the product distribution in the abiotic transformation of TCE by FeS will be investigated. In addition, the impact of additional waste constituents, including chelating agents and redox-active metals, on the abiotic transformation of HCA by FeS, iron oxides and iron silicates will be studied. Future biological work will include a detailed examination of product formation during cell mediated CT dechlorination using 14C labeled CT. Desulfobacterium autotrophicum will be used to inoculate sulfate rich media which contains one of a variety of Fe(III) (hydr)oxides with the aim of generating ferrous sulfide solids. Subsequently, the dechlorination reactivity of cell suspensions and ferrous sulfide solids will be examined. We also anticipate setting up several in situ microcosm (ISMs) this Spring at the FT2 training site at the Wurtsmith Air Force Base in Oscoda, MI. Once the ISMs are in place, sulfate reducing conditions will be stimulated and HCA will be injected and reductive dechlorination activity monitored for up to 120 days.Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 48 publications | 5 publications in selected types | All 5 journal articles |
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Type | Citation | ||
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Butler EC, Hayes KF. Kinetics of the transformation of trichloroethylene and tetrachloroethylene by iron sulfide. Environmental Science & Technology 1999;33(12):2021-2027. |
R825958 (1998) R825958 (2000) R825958 (Final) R826235 (2000) |
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Supplemental Keywords:
reductive dechlorination, iron sulfide, reduced iron minerals, TCE, PCE, CT, desulfobacterium autotrophicum, Geobacter metallireducen, RFA, Scientific Discipline, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Chemical Engineering, Bioavailability, Environmental Chemistry, Fate & Transport, Ecology and Ecosystems, Ecological Risk Assessment, Bioremediation, fate and transport, dechlorination, contaminants in soil, contaminant release, contaminated aquifers, chlorinated solvents, metal compounds, heavy metalsProgress 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.