Innovative Technologies for Remediation of Haloorganics

Gas-phase transfer device.

Background
Innovative technologies are needed for economic remediation of soils and groundwater contaminated with chlorinated solvents. These are among the most common contaminants at United States Superfund sites. Electrolytic reactors and thermocatalytic reaction strategies offer low-cost methods for rapid, complete conversion of such compounds to innocuous gas- or aqueous-phase products. The mechanisms and kinetics of transformations in such reactors are not completely known.

Goal
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.

Objectives
1. To design, optimize and evaluate a variety of continuous-flow reactors that can be used for field-scale groundwater remediation applications.

2. To improve electrode materials and extend reactor design for treatment of semi-volatile chlorinated organic compounds in the gas phase.

3. To investigate novel technologies including the nonelectrolytic, platinum-catalyzed reduction of heavily chlorinated aliphatic compounds by hydrogen and other reductants.

Significant Findings
1. Conversion kinetics for target contaminants in electrolytic reactors usually arise from charge transfer requirements in low-ionic-strength solutions (like potable water). In our work, such limits are avoided through the use of high surface area cathode materials (porous copper foam) and a concentric electrode arrangement with the anode surrounding the cathode. The technology can be used to treat groundwater contaminated with solvents like trichloroethene (TCE).

2. Gas-phase solvents like those in waste streams derived from soil vapor extraction can be rapidly destroyed via thermocatalytic reduction on a variety of metal catalysts. Hydrogen gas is a suitable reductant for the process. Others are under investigation. Half times for solvent destruction are on the order of a few seconds. Gas-phase oxygen can be added to the reaction system to delay the onset of catalyst poisoning indefinitely.

3. The cost of reductant (e.g. hydrogen gas) can make thermochemical reduction of gas-phase solvents in air infeasible. A fuel cell adaptation can be used, however, to meter hydrogen gas for the gas-phase reduction of target solvents like TCE.

Publications

Contact
Robert Arnold
rga@engr.arizona.edu
520-621-2410