Reductive Dechlorination of 1,2-Dichloroethane in a Reactive Iron Barrier

摘要

In February 1999, Orica Australia Pty Ltd installed a pilot-scale reactive iron barrier (RIB) to evaluate the effectiveness of zero valent iron (ZVI) in destroying dissolved-phase chlorinated hydrocarbons (CHCs). The first 13 months of performance monitoring (Stening et al., 2000) showed significant reduction of most CHCs with total influent concentrations up to 220 mg/L, but, as expected, little reduction of the 10 mg/L of 1,2-dichloroethane (1,2-DCA). The inability of ZVI to degrade 1,2-DCA has been his- torically recognized as a limitation of RIBs. However, recent sampling of the pilot-scale RIB has shown that 1,2-DCA degradation is now occurring. Sampling in November 2006 (month 91) confirmed this with concentration reductions of up to one or two orders of magnitude. Groundwater conditions have changed markedly in the test site, largely due to groundwater extraction and treatment starting up within the last two years altering plume flow directions. Most CHCs have decreased to a total of less than 60 mg/L, but 1,2-DCA concentrations have risen to up to 127 mg/L. CHC degradation rates have decreased little since 1999, and gradual fouling is not yet enough to impair RIB hydraulics. The cause of the 1,2-DCA mass removal is due to microbial colonisation of the barrier by dehalores- piring and/or hydrogen utilising bacteria, including Dehalococcoides and Dehalobacter. Although this phenomenon has been observed at the laboratory scale for other com- pounds (e.g., Scherer et al., 2000), this is the first instance the authors are aware of that documents this in the field for 1,2-DCA. Exploiting this phenomenon might broaden the capability of RIBs to reductively dechlorinate hitherto recalcitrant dissolved phase com- pounds.