Article Cite This: Environ. Sci. Technol. 2018, 52, 13747−13755
pubs.acs.org/est
Mechanisms for Abiotic Dechlorination of Trichloroethene by Ferrous Minerals under Oxic and Anoxic Conditions in Natural Sediments Charles E. Schaefer,*,† Paul Ho,‡ Erin Berns,§ and Charles Werth§ †
CDM Smith, 110 Fieldcrest Avenue, #8, 6th Floor, Edison, New Jersey 08837, United States CDM Smith, 14432 SE Eastgate Way #100, Bellevue, Washington 98007, United States § University of Texas at Austin, Civil, Architectural, and Environmental Engineering, 301 E. Dean Keeton Street, Stop C1786, Austin, Texas 78712, United States
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S Supporting Information *
ABSTRACT: Bench-scale experiments were performed on natural sediments to assess abiotic dechlorination of trichloroethene (TCE) under both aerobic and anaerobic conditions. In the absence of oxygen (99.5% purity) and gas standards (methane, ethane, ethene, acetylene, propane, propylene, methyl acetylene, butane in a nitrogen balance) were purchased from Sigma-Aldrich (St. Louis, MO). A solution consisting of 5 mM CaCl2 was used in all the batch experiments to serve as background electrolyte. Five natural aquifer solids used for this study, hereafter referred to as sediments, were collected from US Department of Defense facilities. All sediments were collected from the saturated zone via direct push drilling, then sent overnight to the laboratory where they were stored anaerobically at 3 °C. Prior to use in the abiotic batch experiments, sediments were sterilized via gamma irradiation (2.5 M-rads) to limit microbial activity. Sediments were homogenized by hand in a glass bowl within the anaerobic chamber; any large solids (>5 mm) present in the sediments were discarded. Batch Abiotic Dechlorination ExperimentsAnaerobic. Batch experiments to assess and quantify TCE abiotic dechlorination under anaerobic conditions were performed based on previously described methods.10 Briefly, all preparations were performed in an anaerobic chamber. For each batch system, 5 g of gamma-irradiated sediment was placed in 40 mL amber glass vials. The 5 mM CaCl2 electrolyte solution was sparged with nitrogen gas for a minimum of 1 h prior to use in the anaerobic chamber. A contaminant spiking solution was also prepared using neat TCE dissolved into 5 mM CaCl2 that had been sparged with nitrogen. Control bottles (no added TCE) were amended with 35 mLs of the TCE-free electrolyte, while TCE spiked bottled received 15 mLs (each) of both the TCE-free and TCE-spiked electrolyte; no neat TCE was transferred to the 40 mL vials. TCE aqueous 13748
DOI: 10.1021/acs.est.8b04108 Environ. Sci. Technol. 2018, 52, 13747−13755
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