ABSTRACT

Reductive Dechlorination by Soils and Soil Minerals

Chlorinated hydrocarbons are one of the main groups of sub-surface contaminants in the U.S. Available remedial technologies for the treatment of this contamination such as pump-and-treat often fail to meet remedial goals and they are very expensive. Attractive alternatives to these remedial technologies are those that have low costs because they remove contaminants without extensive changes at the site. Natural attenuation is one such remedial approach. One of the mechanisms that cause natural attenuation is abiotic reductive dechlorination accomplished by redox-active soil components such as iron oxide, iron sulfide, green rust, and Fe(II) bearing clays. Remedial technologies based on abiotic reduction can be low in cost and applicable to situations that are not suitable for bioremediation because of toxicity. This project will improve understanding of these processes to extend the applicability of natural attenuation as well as to provide the basis for the development of alternative remedial technologies. This project is very timely due to the trend toward more low cost-oriented remediation and the potential of the project to apply the growing amount of scientific research to develop new remediation technologies and to improve existing ones.

The overall goal of the project is to characterize abiotic reductive dechlorination system using soil minerals (magnetite, pyrite, green rust, biotite, smectite, and vermiculite) and soils (three types of synthetic soils and three types natural soils) in order to develop remedial technologies and waste treatment systems. The effects of reductants (ferrous iron, dithionite) will be investigated in their ability to convert soil minerals and soils to an active state for the degradation of tetrachloroethylene (PCE), trichloroethylene (TCE), and their degradation products (dichloroethylene isomers (DCEs), vinyl chloride (VC), and chlorinated acetylenes (CAs)). To achieve this goal, four specific objectives are proposed. First, analytical and experimental procedures will be developed to perform laboratory experiments and computer modeling. Second, reductive degradation of selected chlorinated organics by the redox-active soil minerals will be characterized using batch slurry reactors. Third, reductive degradation of the soils will be characterized using both batch slurry reactors and continuous flow columns. Fourth, a model will be developed to predict the fate of target organics. Kinetics of degradation of target chlorinated organics will be measured and the data will be used to develop predictive models of the system.

Successful completion of this project will provide data that can be used to evaluate the potential for extending natural attenuation by promoting abiotic reductive dechlorination and for applying abiotic reductive dechlorination in solely abiotic remedial technologies that 1) produce a reduced zone of soil that act as a semi-passive reactive barrier to groundwater contaminated with chlorinated organics, 2) treat soils with non-aqueous phase contaminants, or 3) treat contaminated groundwater and industrial waste water in above ground systems.