Type of Document Master's Thesis Author Kelly, Catherine Aileen URN etd-09202006-140436 Title Evaluation of Anaerobic Biodegradation of Organic Carbon Extracted from Aquifer Sediment Degree Master of Science Department Environmental Sciences and Engineering Advisory Committee
Advisor Name Title Widdowson, Mark A. Committee Chair Novak, John T. Committee Co-Chair Vikesland, Peter J. Committee Member Keywords
- organic carbon
Date of Defense 2006-09-06 Availability restricted AbstractIn conjunction with ongoing studies to develop a method for quantifying potentially biodegradable organic carbon (Rectanus et al 2005), this research was conducted to evaluate the extent to which organic carbon extracted using this method will biodegrade in anaerobic environments. The ultimate goal is to use this method for the evaluation of chloroethene contaminated sites in order to estimate the long-term sustainability of monitored natural attenuation (MNA) as a remediation strategy. Although relatively recalcitrant under aerobic conditions, the breakdown of chlorinated solvents primarily occurs through the anaerobic process of reductive dechlorination. The biodegradation of organic carbon in these anaerobic environments drives the system to reducing conditions conducive for reductive dechlorination. The extraction procedure developed by Rectanus et al. (2005) has been tested in several series of aerobic bioassays to determine the biodegradable fraction of carbon extracted. This study seeks to show that the carbon removed from the sediment by this extraction process will also degrade in anaerobic environments.
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.
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