A method for quantifying bioavailable organic carbon in aquifer sediments
The fact that naturally occurring microorganisms can biodegrade PCE and TCE allows the use of monitored natural attenuation (MNA) as a remediation strategy at chlorinated solvent-contaminated sites. Research at numerous chlorinated solvent sites indicates an active dechlorinating microbial population coupled with an ample supply of organic carbon are conditions needed to sustain reductive dechlorination. A series of extraction experiments was used to compare the ability of the different extractants to remove organic carbon from aquifer sediments. The different extractants included pyrophosphate, sodium hydroxide, and polished water. Pyrophosphate served as a mild extractant that minimally alters the organic structure of the extracted material. Three concentrations (0.1, 0.5, and 1%) of pyrophosphate extracted 18.8, 24.9, and 30.8% of sediment organic carbon, respectively. Under alkali conditions (0.5 N NaOH), which provided the harshest extractant, 30.7% of the sediment organic carbon was recovered. Amorphous organic carbon, measured by potassium persulfate oxidization, consisted of 44.6% of the sediment organic carbon and served as a baseline control for maximum carbon removal. Conversely, highly purified water provided a minimal extraction control and extracted 5.7% of the sediment organic carbon. The removal of organic carbon was quantified by aqueous TOC in the extract and residual sediment organic carbon content. Characterization of the organic carbon extracts by compositional analysis prior and after exposure to the mixed culture might indicate the type organic carbon and functional groups used and/or generated by the organisms. This is an abstract of a paper presented at the 8th International In Situ and On-Site Bioremediation Symposium (Baltimore, MD 6/6-9/2005).