Grantee Research Project Results

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: R825958
Title: 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 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

Description:

Reductive dechlorination processes play a significant role in the transformation of chlorinated solvents in contaminated aquifers under sulfate- and iron-reducing conditions. Both reduced-iron minerals and microbial systems have shown the potential for facilitating these transformations. Yet, the relative importance of biotic and abiotic pathways, in general, and specifically under representative mixed-waste conditions has been largely unexplored. As such, 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.

Approach:

To achieve this objective, reductive dechlorination of hexachloroethane (HCA) and chloroethylenes will be investigated in the presence and absence of reduced solids, microorganisms, and other waste constituents. Reduced minerals with known surface properties will be generated in the laboratory (e.g., mackinawite FeS(1-x), and magnetite Fe3O4). Microorganisms and naturally reduced aquifer solids will be obtained from contaminated subsurface environments at Wurtsmith AFB and St. Joseph (MI) where intrinsic dechlorination has been occurring under predominantly iron-reducing and sulfidogenic/methanogenic conditions. Parallel chemically-inhibited and unamended in situ microcosms (ISMs) will be installed in the relevant redox zones at Wurtsmith AFB, spiked with HCA and chloroethylenes, and other waste constituents and monitored for product formation and redox conditions for up to six months. In the laboratory batch systems, the rates and product formation of abiotic dechlorination will be investigated with reduced solids in sterile systems and compared to those observed in liquid cultures of iron-reducing and sulfate-reducing microbial enrichments. Temperature and pH effects on dechlorination rates will be evaluated as a means to investigate the relative contributions of abiotic and biotic mechanisms to dechlorination. Liquid- and aquifer-derived mixed cultures will be stimulated using soluble- and solid-electron acceptors, respectively, to assess the impact of the bioavailability of solid-electron acceptors on dechlorination. Relative rates and identification of products will be used to understand the biological rate limitations and pathways. Carefully controlled rate studies of reductive dechlorination by reduced solids will be conducted under a variety of solution conditions to identify reactive surface sites and the rate controlling processes mediated by the reduced-iron surfaces. At various times during the field experiments, the ISMs will be retrieved and analyzed for oxidized and reduced mineral iron species, for comparison with batch systems.

Expected Results:

By comparing the rates and product distribution from this systematic study of abiotic, biotic, and combined dechlorination processes with those obtained under relevant in situ conditions, a clearer picture of the rate-limiting processes will emerge. A comparison to studies with more complex waste mixtures will illustrate if other waste constituents have an impact on product distribution, the controlling process, and rates. Ultimately, the results from this research will contribute to our understanding of how biogeochemical processes and waste-mixture constituents affect the rates and product distribution from reductive dechlorination. Potentially, a detailed knowledge of dechlorination transformation pathways may point to effective ways to manipulate the geochemical setting for optimal and complete transformation of chlorinated solvents to benign end products.

Publications and Presentations:

Publications have been submitted on this project: View all 48 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 5 journal articles for this project

Supplemental Keywords:

reductive dechlorination, bioavailability, mixed-waste, groundwater, chlorinated solvents, PAH, heavy metals, iron sulfide minerals, 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 metals

Progress and Final Reports:

The 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.