Reductive Dechlorination of Trichloroethene Mediated by Humic−Metal Complexes

Abstract

Experiments were conducted to determine if transition metal−humic acid complexes can act as e- transfer mediators in the reductive dechlorination of trichloroethene (TCE) using Ti(III) citrate as the bulk reductant. In the presence of Ni−Aldrich humic acid (AHA) complexes, TCE reduction was rapid, with complete removal of TCE in less than 23 h. Cu−AHA complexes were less effective as e- mediators than Ni−AHA complexes; only 60% of TCE was reduced after 150 h. Partially dechlorinated intermediates were observed during TCE reduction; however, they were transitory, and at no time accounted for more than 2% of the initial TCE mass on a mole C basis. Ethane and ethene were the primary end products of TCE reduction; however, a suite of other non-chlorinated hydrocarbons consisting of methane and C3 to C6 alkanes and alkenes were also observed. The results suggest that humic−metal complexes may represent a previously unrecognized class of electron mediators in natural environments.