Grantee Research Project Results
2000 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, 1999 through November 16, 2000
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 project 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, the major focus of effort was to: (1) perform reductive dechlorination studies in mixed-waste (i.e., chlorinated solvent-metal) systems; (2) compare the relative reactivity and product distributions for magnetite and mackinawite (FeS), solids representative of iron and sulfate reducing conditions; and (3) perform studies of chlorinated solvent by an iron-reducing bacterium, Geobacter metallireducens.
Although mixed metal-organic solvent waste mixtures are common, and the impact of waste mixtures on reductive dechlorination by reduced iron mineral solids was unknown, we undertook a set of screening experiments to establish if and how such mixtures may change the rates of dechlorination in model abiotic mineral systems. FeS and hexachloroethane (HCA) were selected for this study. This choice was predicated on the basis of the well-known pathways for FeS, mediated reductive dechlorination, and the relatively fast rate of reaction of HCA by FeS, (half-life at pH of 7 of less than 2 hours), which would allow for many systems to be screened in a relatively short period of time. The metals investigated included the metal cations cobalt, Co(II), nickel, Ni(II), copper, Cu(II), zinc, Zn(II), silver, Ag(I), cadmium, Cd(II), mercury, Hg(II), manganese, Mn(II), and chromium, Cr(III) as well as the oxyacids of arsenic, As(V), selenium, Se(VI), and chromium, Cr(VI). The intermediate to soft metal acids investigated (Co(II), Ni(II), Cu(II), Zn(II), Ag(I), Cd(II), and Hg(II)), with the exception of Zn(II), showed enhanced rates of the HCA reductive dechlorination. This was attributed to the formation of solid solutions when these metals combine with FeS, which leads to an even more favorable electron transfer reaction. The hard metal acids investigated (Mn(II), Cr(III)) decreased reductive dechlorination rates of HCA. This was attributed to the formation of a passivating metal hydroxide coating of FeS by these sorbed metals. Each of the oxyacids tested (SeO32-, H3AsO3, CrO) in this study resulted in a decreased dechlorination rate of HCA. This occurred due to a complete reduction reaction between the redox active oxyacids and FeS, resulting in a depletion of the electrons available for reductive dechlorination. These results illustrate that in mixed metal-solvent systems, dramatic changes in reductive dechlorination reaction rates by FeS may occur, due to the changes in the surface properties and surface reactions that occur in the presence of metals. However, the impacts of metal were only significant when the concentrations of metals were relatively high (0.01 moles per liter (M)) compared to the FeS concentration, indicating that trace amounts (< 0.0001 M) of metals in relatively uncontaminated sites may not significantly change the rates of dechlorination by FeS.
The relative reactivity of reduced iron minerals produced under iron and sulfate conditions in abiotic systems were investigated using the two primary solids expected under these conditions, magnetite. Significant reductive dechlorination by mackinawite occurred under iron and sulfate reducing conditions, but the relative rates and range of compounds were quite different. In general, the surface area normalized pseudo first order rate constants for FeS systems were more than 1,000 times faster compared to Fe3O4 for similar compounds, e.g., HCA and carbon tetrachloride (CT). In addition, FeS was found to dechlorinate a much wider range of chlorinated compounds than Fe3O4, with Fe3O4 only able to dechlorinate the more fully chlorinated compounds such as HCA and CT. Furthermore, FeS was able to completely dechlorinate compounds such as tetrachlorethylene (PCE) and trichloroethene (TCE), but these same compounds showed no reaction with Fe3O4.
These results indicate that sulfate-reducing conditions in the presence of iron can generate a more favorable solid (FeS) for effective dechlorination than iron-reducing conditions. These results also point to the potential for utilizing sulfate-reducing bacteria or chemical-reducing methods, when iron or sulfate are present or added, for generating an effective reactive material (FeS) for in situ remediation.
For selected systems, a full range of dechlorination products were identified and monitored during the course of the dechlorination rate studies. It was hoped that product identification would help delineate important abiotic dechlorination pathways and also might allow abiotic and biotic pathways to be distinguished in the case where nonbiotic products were identified. The FeS was a much more effective reducing agent for a wide range of compounds compared to Fe3O4. FeS is capable of completely dechlorinating 1,1,2,2-tetrachloroethane (PCA), HCA, PCE, and TCE through a pathway that ultimately leads to the production of acetylene as a major end product. In the case of CT, FeS also was effective, leading to the nearly complete dechlorination and the suspected but not identified CS2. In the case of magnetite, dechlorination was only accomplished for CT and HCA. Complete dechlorination was only possible for CT. A dechlorination pathway leading to the formation of carbon monoxide (CO) as a major product was discovered, as in the case of the CT declorination by Fe3O4. Based on these findings, and the implied predominance of sequential dechlorination pathways and products by microorganisms, a means to distinguish abiotic from biotic pathways was implicated through the product distribution studies. For sites contaminated with chlorinated ethylenes such as PCE and TCE, the presence of acetylene is a strong indication that an abiotic pathway mediated by FeS is occurring. Likewise in the case of CT contaminated sites, the presence of CS2 or CO is strong circumstantial evidence that abiotic pathways involving FeS or Fe3O4 are playing an important role in the transformation of chlorinated compounds. A demonstration of the mechanism of dechlorination by an iron-reducing bacterium was performed using the dissimilatory iron-reducing bacteria, G. metallireducens, in the presence of CT. The results demonstrate that the dissimilative iron-reducing bacteria G. metallireducens directly transforms CT, and that the rate of transformation is proportional to biomass. The kinetics of transformation were found to conform to a two-site Michaelis-Menten expression. The biologically mediated reaction formed chloroform (CF) as a minor product (14-25 percent), and the major product was an apparent trichlorocarbon species irreversibly bound to cell material (75-86 percent). Mutual inhibition effects observed during Fe(III)-citrate and CT reduction, and the specific labeling of membrane proteins by 14CT, suggested that CT is transformed by G. metallireducens via co-metabolic mechanisms at sites located within the cells' membranes.
Future Activities:
In the upcoming project period, the major focus will be to: (1) complete laboratory work related to abiotic and biotic dechlorination studies under iron- and sulfate-reducing conditions; and (2) conduct a field experiment of the potential for reductive dechlorination by reduced iron minerals using in situ microcosm.
Journal Articles on this Report : 2 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) |
Exit Exit Exit |
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Butler EC, Hayes KF. Kinetics of the transformation of halogenated aliphatic compounds by iron sulfide. Environmental Science & Technology 2000;34(3):422-429. |
R825958 (2000) R825958 (Final) |
not available |
Supplemental Keywords:
reductive dechlorination, mixed-waste, groundwater, chlorinated solvents, heavy metals, reduced iron minerals, iron sulfide minerals, iron reducing conditions, sulfate reducing conditions., 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 metalsRelevant Websites:
http://www.engin.umich.edu/dept/cee/research/adriaens/ Exit
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.