Objective(s) of the Research Project: To determine: 1) if humate-induced remediation is a viable and feasible remediation technique, and 2) if it is, determine the primary remediation mechanism, i.e., stimulation of biodegradation, adsorption, or a combination of both. These objectives will be accomplished by: 1) identifying the humate, or humates, with the greatest sorption capacity, and 2) identifying and characterizing the predominant mechanism(s) of the humate-induced remediation process(es) using microcosms containing either pristine or contaminated surface soil collected from a petroleum drilling field near Oklahoma City, OK.
Progress Summary/Accomplishments:
Adsorption processes:
Rock Eval pyrolysis experiments conducted in the second quarter demonstrated that humate #2 retained approximately 25% of its mass as adsorbed petroleum after exhaustive methanol/dichloromethane extraction. This result was independently verified in the third quarter using gravimetric methods. Gravimetric results showed that humate #2 retains 9 to 13 % of its mass as adsorbed petroleum after exhaustive methanol/dichloromethane extraction.
Adsorption of the aromatic compounds present in the petroleum, by humate #2, is being further examined in order to understand the fate of these potentially harmful compounds. The microcosm organic solvent extracts were reanalyzed with GC/MS using select ion monitoring (SIM) at m/z = 77 and 78. To date, microcosms (Days 2, 10, 38, and 68) containing field-contaminated soil with fresh petroleum have been examined. By day 2, adsorption of benzene, alkylated monoaromatics, naphthalene, and alkylated naphthalenes is detected. Day 38 and 68 microcosm samples containing humate #2 show a 33 to 50% decrease of the extractable benzene, alkylated monoaromatics, naphthalene, and alkylated naphthalenes relative to control microcosms without humate. We are now examining microcosms from days 142 and 206, as well as microcosms containing pristine soil and fresh petroleum, with and without humate. As well, using pyrolysis GC/MS, we are analyzing the microcosm residues after extraction in attempts to detect the adsorbed benzene, alkylated monoaromatics, naphthalene, and alkylated naphthalenes compounds in order to confirm that humate adsorption of these compounds is indeed occurring. These results are being used to design experiments testing the adsorption capacity of humates for refined petroleum products such as gasoline. These experiments are part of the proposed research in our submitted preproposal to IPEC.
Biodegradation processes:
Microcosm results (n-C17/pristine and n-C18/phytane ratios) indicate that by day 142, biodegradation is clearly accelerated in microcosms (both field-contaminated soil, or field-contaminated soil with fresh petroleum added) containing humates relative to microcosms without humate #2. Kinetic parameters, i.e., degradation rate constants will be calculated from the experimental data. Even by day 142, no biodegradation in microcosms containing pristine soil + fresh petroleum is observed. It is hypothesized that the pristine soil does not contain petroleum-degrading microflora. To test this hypothesis, we inoculated the remaining pristine soil and fresh petroleum microcosms with 2 mL of field-contaminated soil and will allow them to incubate for approximately 60 – 90 days before analysis.
Humate characterization:
Pyrolysis GC/MS (py-GC/MS) and thermochemolysis GC/MS (using tetramethylammonium hydroxide) (TMAH-GC/MS) have been used to characterize the organic structure and composition of humate #2. Both analytical methods chemically and/or thermally degrade the macromolecular structure into smaller molecular fragments amenable to GC/MS analysis. Characterization of the chemical composition of humates will provide greater understanding and predictive capacity for identifying and characterizing adsorption processes of aliphatic and aromatic compounds present in petroleum by humates.
Py-GC/MS results provide a suite of monoaromatic compounds containing a variety of methyl, hydroxyl, and methoxy functional groups, indicating that lignin is an organic precursor of humates. In addition, linear alkanes, and the corresponding 1-alkenes, are also detected in substantial amounts. The TMAH-GC/MS analysis is relatively selective for lignin-type components, as well as fatty acids. TMAH results also confirm lignin precursors, showing that humate #2 predominantly consists of guiacyl and cinnamyl structures. The presence of these structures, and the absence of syringyl structures, suggests that monocotyledonous angiosperms were the predominant plant material that served as the precursor to humate #2. Three other humates (#5, 7, and 8) will also be characterized by these methods.
Publications/Presentations:
Future Activities:
Supplemental Keywords: Adsorption, biodegradation, humate