The proposed project will determine the mechanism and kinetics of transformations of low-molecular-weight-chlorinated aliphatic compounds in a variety of gas- and liquid-phase electrolytic reactors. Electrolytic reduction of such compounds, e.g. trichloroethylene, is a reasonable extension of reductive dehalogenations involving zero-valent metals that avoids potential problems in non-electrolytic systems such as metal dissolution and/or passivation. Furthermore, because the redox potential of reactive surfaces can be manipulated in an electrolytic system, these reactions can produce much higher area-specific rates for the reactions of interest or minimize rates of competitive reactions such as generation of hydrogen from water. In previous work we established the feasibility of aqueous-phase transformations of chlorinated alkenes and alkanes to innocuous products. TCE was reduced to primarily ethene and ethane, or, alternatively, oxidized to a mixture of carbon dioxide and carbon monoxide (as the reactor anode). Project extension with permit us to design, optimize and evaluate a variety of continuous-flow reactions that can be used for field-scale groundwater remediation applications. Other project objectives include the improvement of electrode materials and the extension of reaction design for treatment of semi-volatile chlorinated organic compounds in the gas phase. As envisioned, gas- phase electrolytic reactors would be used to treat halogenated residues in the contaminated vadose zone gases that are brought to the surface during remediations based on soil vapor extractions. Aqueous-phase reactors can be adapted for use in wells so that contaminated ground waters need not be pumped to the surface for treatment. Other novel technologies under investigation within the overall project include the non-electrolytic, palladium-catalyzed reduction of heavily chlorinated aliphatic compounds by zero-valent metals and the photoinitiated destruction of such compounds in a two-solvent system consisting of any of a variety of alcohols and ketones. The latter (photoinitiated) system can be used to remove halogenated, semi-volatile organics from a contaminated gas stream and destroy them in the alcohol/ketone solvent mixture. The process can be driven by sunlight although only a small fraction of sunlight that reaches the earth's surface drives the necessary reactions.
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