Benzene oxidation under sulfate-reducing conditions in columns simulating in situ conditions
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The oxidation of benzene under sulfate-reducing conditions was examined in column and batch experiments under close to in situ conditions. Mass balances and degradation rates for benzene oxidation were determined in four sand and four lava granules filled columns percolated with groundwater from an anoxic benzene-contaminated aquifer. The stoichiometry of oxidized benzene, produced hydrogen carbonate and reduced sulfate correlated well with the theoretical equation for mineralization of benzene with sulfate as electron acceptor. Mean retention times of water in four columns were determined using radon (222Rn) as tracer. The retention times were used to calculate average benzene oxidation rates of 8–36 μM benzene day−1. Benzene-degrading, sulfide-producing microcosms were successfully established from sand material of all sand filled columns, strongly indicating that the columns were colonized by anoxic benzene-degrading microorganisms. In general, these data indicate a high potential for Natural Attenuation of benzene under sulfate-reducing conditions at the field site Zeitz. In spite of this existing potential to degrade benzene with sulfate as electron acceptor, the benzene plume at the field site is much longer than expected if benzene would be degraded at the rates observed in the column experiment, indicating that benzene oxidation under sulfate-reducing conditions is limited in situ.
KeywordsBenzene Degradation Natural attenuation Sulfate-reducing conditions
This work is integrated in the internal research and development program of the UFZ as well as the SAFIRA I project. The authors thank Werner Kletzander, Ralf Trabitzsch and Jörg Ahlheim of the Department of Groundwater Remediation for column sampling and organizational help, and Dietmar Hähnel for analyzing BTEX, sulfide, sulfate and carbonate during the column experiment. Special thanks is addressed to Stephanie Hinke for preparing culture media and analyzing samples of sulfide and benzene during the microcosm experiment.
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