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MICROCOSM STUDY OF ANAEROBIC BIODEGRADATION OF MTBE AND TBA
Citation:
YANG, X., R. KOLHATKAR, J. T. WILSON, C. J. ADAIR, T. KUDER, AND P. PHILP. MICROCOSM STUDY OF ANAEROBIC BIODEGRADATION OF MTBE AND TBA. Presented at 2005 NGWA Conference of MTBE and Perchlorate: Assessment, Remediation, and Public Policy, San Francisco, CA, May 26 - 27, 2005.
Impact/Purpose:
To inform the public.
Description:
Ground water samples collected in at a gasoline spill sites in Orange County, California, suggested that MTBE was being transformed to TBA. In some of the most heavily contaminated wells, the concentration of TBA was higher than the concentration of MTBE (MTBE 2 µg/L and TBA 40,000 µg/L, MTBE 3 µg/L and TBA 14,300 µg/L, MTBE <1 µg/L and TBA 1730 µg/L). Analysis of stable carbon isotopes in MTBE in ground water in these wells indicated that MTBE was being biologically degraded (δ13C= +27.0, -18.63 and -15.0 respectively). In one heavily contaminated well the concentration of MTBE and TBA were essentially equivalent (MTBE 1840 µg/L and TBA 1660 µg/L), and there was no evidence from stable carbon isotopes that MTBE had been biodegraded (δ13C= -28.9). Sediments were collected from the site for a microcosm study. Microcosms were prepared in an anaerobic glove box under an atmosphere containing 5 to 7% hydrogen. They were incubated at room temperature. The removal of MTBE in the microcosms was rapid; within two months the initial concentration of MTBE (1.2 mg/L) was depleted to the analytical detection limit (<0.003 mg/L). The first order rate of MTBE biodegradation was 32/year. As the MTBE was removed from the pore water of the microcosms, an equivalent amount of TBA was produced. After complete removal of the MTBE, the pore water in the microcosms contained low concentrations of methane (0.17 mg/L) and higher concentrations of sulfate (390 mg/L). There was no evidence of TBA biodegradation in the microcosms. Ground water samples collected in at a gasoline spill sites in Orange County, California suggested that MTBE was being transformed to TBA. In some of the most heavily contaminated wells, the concentration of TBA was higher than the concentration of MTBE (MTBE 2 µg/L and TBA 40,000 µg/L, MTBE 3 µg/L and TBA 14,300 µg/L, MTBE <1 µg/L and TBA 1730 µg/L). Analysis of stable carbon isotopes in MTBE in ground water in these wells indicated that MTBE was being biologically degraded (δ 13C= +27.0, -18.63 and -15.0 respectively). In one heavily contaminated well the concentration of MTBE and TBA were essentially equivalent (MTBE 1840 µg/L and TBA 1660 µg/L), and there was no evidence from stable carbon isotopes that MTBE had been biodegraded (δ13C= -28.9). Sediments were collected from the site for a microcosm study. Microcosms were prepared in an anaerobic glove box under an atmosphere containing 5 to 7% hydrogen. They were incubated at room temperature. The removal of MTBE in the microcosms was rapid; within two months the initial concentration of MTBE (1.2 mg/L) was depleted to the analytical detection limit (<0.003 mg/L). The first order rate of MTBE biodegradation was 32/year. As the MTBE was removed from the pore water of the microcosms, an equivalent amount of TBA was produced. After complete removal of the MTBE, the pore water in the microcosms contained low concentrations of methane (0.17 mg/L) and higher concentrations of sulfate (390 mg/L). There was no evidence of TBA biodegradation in the microcosms.