Evaluation of Anaerobic Biodegradation of Organic Carbon Extracted from Aquifer Sediment
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Three aquifer sediment samples characterized by low, medium, and high carbon concentrations were taken from Naval Submarine Base Kings Bay, Georgia. Two sites were also sampled from Naval Amphibious Base Little Creek, Virginia. MLS20 is a site located inside of a chloroethene plume, and MLS10 is located outside of the plume. For approximately 12 weeks aqueous total organic carbon (TOC), headspace carbon dioxide (CO2), volatile fatty acids (VFAs), and headspace hydrogen concentrations were monitored for evidence of the biodegradation of organic carbon. Although few VFAs were observed throughout the experiments, their presence as early as 8 days after inoculation indicated that the bioassays were anaerobic. The fewest VFAs were seen in the MLS20 bioassays, while the most VFAs were observed in the MLS10 bioassays. MLS20 exhibited low levels of TOC loss and the low VFA levels indicate that complex organic matter was not highly degraded in these bioassays. The higher level of VFAs observed in MLS10 bioassays corresponded with little TOC degradation, indicating that although more complex organics were being broken down, conditions were not reduced enough to further oxidize the organic carbon. As much as 50% TOC loss was observed in the Kings Bay bioassays with few VFAs detected.
Loss of TOC was accompanied by CO2 generation which provides supporting evidence that organic carbon was being oxidized. Hydrogen was observed in the bioassays, suggesting that VFAs resulting from organic carbon breakdown were being oxidized. This indicates that organic carbon removed from sediment using the extraction process is biodegraded anaerobically and could lead to conditions capable of sustaining reductive dechlorination.
- Masters Theses