EPA Grant Number: R827015-01-0
Title: Anaerobic Intrinsic Bioremediation of Whole Gasoline
Investigators: Joseph Suflita
Institution: University of Oklahoma
EPA Project Officer: Bala Krishnan
Project Period: February 1, 1999 to January 31, 2000 (N/C Ext. to
February 28, 2001)
Project Amount: $130,036
Research Category: Intrinsic bioremediation/natural attenuation
The major accomplishments of this quarter were:
The first large set of hydrocarbon data from the Purge and Trap/GC/MS analysis was generated for time 0, 40, 112, and 180 days. In order to standardize the data, a internal conserved standard (i.e. a component of the gasoline that is present but not degraded) is required; 1,1,3-trimethylcyclohexane was selected for this purpose.
The success of our proposed research is dependent upon the Ft. Lupton sediments expressing a broad range of biodegradative activities towards hydrocarbons. Our initial hydrocarbon analysis has shown this assumption to be true. Alkane, alicyclic, and aromatic compounds were all biodegraded concurrently under both sulfate-reducing and methanogenic conditions over the initial 180 day incubation period with much greater activity seen in the presence of sulfate. Nitrate-amended incubations continue to show no signs of significant hydrocarbon loss over the sterile controls.
Of the aromatic constituents of gasoline that we have examined, toluene appears to be the most biodegradable with 100% loss within 40 days of incubation under sulfate-reducing conditions and 112 days of incubation under methanogenic conditions. Distinct patterns of xylene and ethylbenzene biodegradation were seen, dependent upon the dominant terminal electron-accepting process. Under sulfate-reducing conditions, o- and m-xylene were completely biodegraded, but p-xylene and ethylbenzene appeared recalcitrant. Under methanogenic conditions, only o-xylene was completely biodegraded with m-xylene, p-xylene, and ethylbenzene exhibiting only 30-40% biodegradation over the 180 day incubation period. Similarly, C-3 and C-4 benzenes were more susceptible to biodegradation under sulfate-reducing conditions with 40-60% loss compared to 20-30% under methanogenic conditions.
Data for the n-alkanes gasoline components present in the gasoline show that these compounds are also biodegraded under both methanogenic and sulfate-reducing conditions by the resident microbiota at Ft. Lupton. The anaerobic biodegradation of n-alkanes linked to methanogenesis has only recently been reported. Similar to the aromatic hydrocarbons, n-alkanes were biodegraded to a greater extent under sulfate-reducing conditions with n-heptane, n-octane, and n-nonane completely consumed after 180 days; n-hexane and n-pentane showed around 95 and 70 % disappearance, respectively. Much less biodegradation of the n-alkane fraction was observed under methanogenic conditions with only n-nonane and n-octane being more than 90% biodegraded. n-Heptane biodegradation was intermediate at around 70%, and both n-pentane and n-hexane were not biodegraded under methanogenic conditions. These results demonstrate diverse biodegradative abilities of the microorganisms within the Ft. Lupton sediment and that both the rate and extent of biodegradation is dependent upon the availability of sulfate as a terminal electron acceptor.