Conduct investigation into the prospect for whole gasoline degradation under anaerobic conditions.
We have been continually monitoring the susceptibility of whole gasoline to decay under methanogenic, sulfate- reducing, and nitrate-reducing conditions in ongoing, extended incubations. Although high rates of endogenous methanogenesis and sulfate reduction have been observed in the first calendar year, to date, no stimulation has been seen due to the initial 10 l gasoline amendment. Nitrate-amended microcosms have demonstrated little nitrate reduction or hydrocarbon biodegradation. These and previous findings indicate that this terminal electron acceptor does not play a significant role in petroleum metabolism at this site.
We have begun to analyze the extensive hydrocarbon data from the first six months of these incubations. There are significant differences between the amounts of analytes detected in the aqueous phases under different terminal electron accepting-conditions; this may reflect differential partition to the solids.
Overall, our preliminary findings indicate much greater biodegradation under sulfate-reducing conditions than under methanogenic conditions by the indigenous microbiota at the Ft. Lupton site. A wide range of aromatic, alicyclic, and alkane substrates were degraded under sulfate-reducing conditions, surprisingly with most of the degradation occurring in the first 40 days of incubation. Branched alkanes were much more resistant to biodegradation than straight chain alkanes. Also, BTEX compoundswere selectively degraded under sulfate-reducing and methanogenic conditions. Of the xylene isomers, the meta- and ortho- isomers were more labile than the para-isomerunder sulfate-reducing conditions. Under methanogenic conditions, the para- and meta-isomers were preferred over the orth-isomer. Benzene clearly appears to be the most recalctrant of the BTEX isomers.
Parallel experiments, examining the fate of alkane and alicyclic compounds as sole substrates have continued. As in the gasoline experiment, high rates of endogenous methanogenesis and sulfate-reduction have largely masked any stimulation that may have loccurred due to the substrate amendments. However, we have transferred the original incubations into media, and this has resulted in both lower endogenous rates of methanogenesis and sulfate reduction as well as significant stimulation of these process in pentane-, hexane-, octane-, undecane-, and pentadecane- amended. These experiments reveal the ability of the resident microbiota to biodegraded these components commonly found in gasoline and gas condensate and confirm the results found with gasoline as a complex substrate.
Kropp, K.G.; Mormile, M.R.; and Suflita, J.M. 2000. Anaerobic biodegradation of MTBE and alternative gasoline oxygenates. Environmental Protection Agency/American Petroleum Institute MTBE Biodegradation Workshop, February, Cincinnati, OH.
Based upon the residual hydrocarbons remaining in the gasoline incubations after one year of incubation, we requested and were granted a no-cost extension in order to continue monitoring gasoline biodegradation in these incubations over an additional year.
hydrocarbon, biodegradation, bioremediation, methanogenic, sulfate-reducing, nitrate-reducing, BTEX