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University of Arizona

Superfund Research Program

Innovative Technologies for Remediation of Haloorganics

Project Leader: Robert G. Arnold
Grant Number: P42ES004940
Funding Period: 2000-2010

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Project Summary (2000-2005)

The goal of this project is to 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 compounds such as trichloroethylene is a reasonable extension of reductive dehalogenations involving zero-valent metals and avoids the potential problems of 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 reactors can produce much higher area-specific rates for the reactions of interest or minimize rates of competitive reactions such as the generation of hydrogen from water. In previous work, the feasibility of aqueous-phase transformations of chlorinated alkenes and alkanes to innocuous products was established. TCE was reduced to primarily ethene and ethane or, alternatively, oxidized to a mixture of carbon dioxide and carbon monoxide (at the reactor anode). The extension of this project will permit the design, optimization and evaluation of a variety of continuous-flow reactors that can be used for field-scale groundwater remediation applications. Other project objectives include the improvement of electrode materials and the extension of reactor 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 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 nonelectrolytic, 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.

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