GAS PHASE REDUCTION OF CHLORINATED VOCs BY ZERO VALENT IRON

Abstract

The removal of trichloroethylene (TCE) by reduction with elemental iron was examined in batch reactors representing three phase gaseous systems (Fe⁰ (solid), water vapor + TCE vapor + air mixture (gaseous), and condensed water on Fe⁰ surface (aqueous)) and two phase aqueous systems (Fe⁰ (solid), water (aqueous)) as the reaction medium. Two separate removal mechanisms were found for TCE removal in the gas phase reactors: [1] adsorption onto the Fe⁰ surface under low relative humidity (RH), and [2] reaction with Fe⁰ to form other organic compounds, such as ethylene, isomers of dichloroethylene, and vinyl chloride under 100% RH conditions in the gas phase. The adsorption of TCE vapor onto the Fe⁰ surface was fast initially and highest at low temperatures. The reduction reaction of TCE in the gas phase was first order with respect to the TCE concentration remaining in the gas phase under conditions of 100% RH at 15, 22, and 35°C, and the observed reaction rate constant (k _obs) exhibited a maximum at elevated temperatures. The estimated k _obs values for the degradation of dissolved TCE in aqueous systems were the same order of magnitude with the rate constants in the gas phase and exhibited an increasing rate at higher temperatures. The results suggest that Fe⁰ represents an economical choice for vapor phase barriers to limit the spread of contaminants in soil gas and reduce fugitive air emissions from contaminated sites.

Keywords:

• Trichloroethylene
• Gas-phase dechlorination
• Elemental iron
• Relative humidity

Acknowledgments