TCE Bioremediation in a Deep Basalt Aquifer

Finneran, K.T. M. Leahy, and P. J. Zeeb, "TCE Bioremediation in a Deep Basalt Aquifer, "Poster accepted for Battelle Conference on In-Situ and On-Site Bioremediation, June, 2003, Orlando.

TCE biodegradation has not been widely reported in deep, basalt aquifers, relative to shallow sand or silt aquifer material. Basalt microbiology is relatively unknown compared to shallow aquifer environments. TCE bioremediation was investigated in a TCE-contaminated, deep, basalt aquifer beneath a New Jersey industrial facility Site geochemical data indicated that anaerobic microorganisms were active within the deep basalt as evidenced by the concentration of Fe (II) and Mn (II); as well as localized concentrations of sulfide. TCE was the only electron acceptor present at significantly high concentration and, therefore, exerted selective pressure on reductively dechlorinating microorganisms. In situ molecular analyses using Dehalococcoides specific primers indicated that these halorespiring Bacteria were present in several areas of the site. The hypothesis that the basalt is electron donor-limited was tested using aquifer material in anaerobic laboratory incubations. Acetate, lactate, methanol, and ethanol were the electron donors tested to determine if the rate and extent of TCE bioremediation can be stimulated with the knowledge that the requisite microorganisms are present, but not necessarily active under the prevailing in situ conditionsAlkaline pH basalt was buffered to determine the effect of pH upon dechlorination. A halorespiring enrichment culture, KB1, was added to basalt aquifer material as well. TCE was completely reduced within 65 days of bioaugmentation in alkaline and neutral basalt aquifer material. Mass balance calculations indicate that approximately 100% of the TCE was converted to ethene. Ethanol and acetate were utilized more efficiently than methanol. TCE was reduced to cis-DCE and VC in the donor-amended, non-bioaugmented incubations, but ethene was not produced. TCE was not removed or transformed in any control incubations. These data indicate that bioremediation of basalt aquifers is stimulated by adding soluble electron donors. Bioaugmentation increased the rate and extent of complete dechlorination, likely due to the lack of microbial competition within basalt aquifer material.

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