SMALL COLUMN MICROCOSM FOR ASSESSING METHANE-STIMULATED VINYL-CHLORIDE TRANSFORMATION IN AQUIFER SAMPLES

A small-column microcosm was designed and operated to evaluate the potential for in-situ Vinyl chloride (VC) biotransformation by a methane-stimulated culture. Microcosms consisted of 15-mL test tubes filled with aquifer material and fitted with a fluid exchange system to allow sequential batch testing. Aquifer material was aseptically obtained from two locations at a chloroethene-contaminated Superfund site in St. Joseph, MI. In microcosm tests, influent VC concentrations ranged from 1 to 17 mg/L (15-275 mu M) with methane concentrations of 0.5-4.0 mg/L (30-250 mu M) and dissolved oxygen concentrations of about 29 mg/L (900 mu M). Stimulation of an active methane-utilizing population occurred within 60 days, and VC transformation was observed in all of the methane-fed microcosms. A maximum amount of VC transformation, independent of influent VC concentration, was observed for each methane concentration used. Significant differences in VC transformation ability was found in the aquifer samples from the two locations. Transformation yields (T-y) of up to 3.5 mg of VC transformed/mg of methane utilized (0.9 mol of VC/mol of CH4) were found atone location compared to a maximum of 1.0 mg of VC/mg of CH4 (0.26 mol of VC/mol of CH4) at the other. Up to 16 mg/L VC (250 mu M) was transformed with an addition of 4 mg/L methane (250 mu M) with no significant toxic effects observed. The microcosms performed well throughout the study, providing consistent repeatable results.