Anaerobic Intrinsic Bioremediation of Whole Gasoline

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

Description:

The major accomplishments of this quarter were:

  1. Continued long-term monitoring of the terminal electron-accepting process in laboratory incubations examining both whole gasoline and weathered crude oil
  2. Analysis by Purge and Trap/GC/MS of the residual hydrocarbons in whole gasoline incubations incubated for 43, 52, 70, and 78 weeks. This analysis revealed extensive biodegradation of the n-alkane and aromatic fractions of gasoline under both methanogenic and sulfate-reducing conditions.
  3. Further demonstration of the n-alkane biodegradative activity in Ft. Lupton sediments through laboratory experiments using these compounds as sole substrates.

Continual monitoring of the dominant terminal electon-accepting processes in these incubations, sulfate reduction and methanogenesis, has shown that the Ft. Lupton sediments posses but active microbial communities and a large amount of endogenous electron donor. This endogenous donor has prevented us from demonstrating any stimulation of anaerobic respiration due to gasoline amendments in the primary incubations.

During this quarter, residual hydrocarbons in samples that had been incubated for 43-78 weeks and subsequently frozen for preservation were analyzed. This analysis showed that the total loss of hydrocarbon from the 10 l gasoline amendment, although higher in sulfate-reducing vs. methanogenic incubations, was relatively constant during this extended incubation. Samples from 43-78 weeks showed 40-45% hydrocarbon loss under sulfate-reducing conditions and approximately 35-40% loss under methanogenic conditions. These results were disappointing, as we had hoped to see continued hydrocarbon depletion down to its most recalcitrant componentsduring this extended incubation. Nitrate-amended incubations continue to show no signs of significant hydrocarbon loss over the sterile controls even after 78 weeks of incubation. These results also suggest that this experiment should be repeated with a lower amount of gasoline in order to see complete biodegradation.

Despite the apparent recalcitrance of some components, we did observe complete biodegradation of some fractions of the gasoline amendment. Notably, n-alkanes of seven carbons or longer were completely biodegraded under both sulfate-reducing and methanogenic conditions. However, hexane was 95% and 50% biodegraded under sulfate-reducing conditions and methanogenic conditions, respectively, while pentane was only 50% and 25% biodegraded under sulfate-reducing conditions and methanogenic conditions, respectively.