Model for In Situ Perchloroethene Dechlorination via Membrane-Delivered Hydrogen

A one-dimensional contaminant fate and transport model was developed to simulate reductive dechlorination of perchloroethene (PCE) in an anaerobic aquifer supplied with hydrogen via a gas-permeable membrane curtain. The model predicted that providing hydrogen at transfer rates equal to the reducing-equivalent demand associated with the groundwater PCE flux would mineralize 75% of the PCE-bound chlorine to chloride and, furthermore, that 0.55 moles of chloride would be released per mole of hydrogen transferred. Supplying higher hydrogen transfer rates was predicted to result in slightly lower dechlorination efficiencies and significantly lower dechlorination yields due to greater methanogenic growth and concomitant displacement of dehalorespirers away from the hydrogen-supply membranes. The model also predicted that high hydrogen-utilizing biomass concentrations would develop near the membranes, resulting in minimal hydrogen dispersal. Model predictions were qualitatively similar to results attained in experimental soil column studies; however, incorporation of homoacetogenesis and acetate utilization by dehalorespirers, as well as hydrogen production via fermentation of biomass decay products, would have improved agreement between model simulations and experimentally observed dechlorination performance.