Grantee Research Project Results
2001 Progress Report: Effect of the Gasoline Oxygenate Ethanol on the Migration and Natural Attenuation of BTEX Compounds in Contaminated Aquifers
EPA Grant Number: R828156Title: Effect of the Gasoline Oxygenate Ethanol on the Migration and Natural Attenuation of BTEX Compounds in Contaminated Aquifers
Investigators: Alvarez, Pedro J.
Institution: University of Iowa
EPA Project Officer: Aja, Hayley
Project Period: June 1, 2000 through May 31, 2002 (Extended to January 31, 2004)
Project Period Covered by this Report: June 1, 2000 through May 31, 2001
Project Amount: $194,878
RFA: Exploratory Research - Engineering, Chemistry, and Physics) (1999) RFA Text | Recipients Lists
Research Category: Water , Air , Safer Chemicals , Land and Waste Management
Objective:
A likely upcoming replacement of MTBE with ethanol as a gasoline oxygenate represents attractive economic and air-quality benefits. However, fuel releases that contaminate the subsurface are likely to continue well into the future. Thus, a basic understanding of how ethanol affects the fate and transport of BTEX in aquifers (and related remediation activities) is needed before a widespread changeover occurs.The objective of this project is to determine: (1) if ethanol enhances BTEX migration in aquifers; (2) how ethanol affects the induction of BTEX-degrading enzymes, and what conditions lead to simultaneous versus preferential degradation of ethanol in the presence of BTEX; and (3) how ethanol affects transitions in electron acceptor conditions. Emphasis will be placed on quantifying the effect of ethanol on BTEX retardation factors, degradation rates, and microbial population shifts. An ancillary objective is to review data from Iowa DNR files to determine if ethanol increases the length of benzene plumes.
Progress Summary:
Aquifer columns were constructed to mimic natural attenuation of petroleum product releases, including transitions in electron acceptor conditions commonly encountered at contaminated sites. These columns are being fed continuously with synthetic groundwater spiked with BTEX and ethanol or MTBE to discern the effect of such oxygenates on the fate and transport of individual BTEX compounds.Both ethanol and MTBE could enhance dissolved BTEX mobility by exerting a cosolvent effect that decreases sorption-related retardation. This effect, however, is concentration-dependent and was not observed when ethanol or MTBE was added (at 1 percent) continuously with BTEX to sterile aquifer columns. Nevertheless, a significant decrease in BTEX retardation was observed with 50 percent ethanol, suggesting that neat ethanol spills in bulk terminals could facilitate the migration of preexisting contamination.
MTBE (25 mg/L) was not degraded in larger nonsterile columns, and it did not affect BTEX degradation. Ethanol (2 g/L), on the other hand, was degraded rapidly and exerted a high demand for nutrients and electron acceptors that could otherwise have been used for BTEX degradation. Ethanol also increased the microbial concentration near the column inlet by one order of magnitude relative to columns fed BTEX alone or with MTBE. However, 16S-rRNA sequence analyses of dominant DGGE bands identified less species that are known to degrade BTEX when ethanol was present.
Overall, the preferential degradation of ethanol and the accompanying depletion of oxygen and other electron acceptors hindered BTEX biodegradation, which suggests that ethanol could increase the length of BTEX plumes.
Future Activities:
We plan to continue operating the columns and to evaluate alternative anaerobic bioremediation alternatives, including biostimulation with nitrate and sulfate addition, and bioaugmentation with a benzene-degrading methanogenic culture provided by Prof. Elizabeth Edwards (University of Toronto).We also have begun to characterize how ethanol affects specific BTEX biodegradation activities using reference strains in model chemostat systems fed different benzene/ethanol mixtures. Emphasis is being placed on determining how ethanol affects the induction of BTX-degrading enzymes and isolating the effect of ethanol on the metabolic flux of benzene. We also will construct and test a mathematical model that integrates the negative effect of ethanol on BTEX metabolic flux with the positive effect related to additional microbial growth. These activities will be summarized in the next annual report.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
| Other project views: | All 34 publications | 13 publications in selected types | All 10 journal articles |
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Da Silva MLB, Alvarez PJJ. Effects of ethanol versus MTBE on benzene, toluene, ethylbenzene, and xylene natural attenuation in aquifer columns. Journal of Environmental Engineering-ASCE 2002;128(9):862-867. |
R828156 (2001) R828156 (Final) |
Exit Exit |
Supplemental Keywords:
risk assessment, groundwater, bioremediation, enzyme activity, MPN, retardation., RFA, Air, Scientific Discipline, Waste, Toxics, Remediation, Engineering, chemical mixtures, HAPS, Environmental Chemistry, 33/50, Engineering, Chemistry, & Physics, EPCRA, Bioremediation, gasoline, Benzene (including benzene from gasoline), BTEX migration, air sampling, electron accpter conditions, ethanol degradation rates, MTBE, contaminated aquifers, benzene, risk assessment, BTEX, biological attenuation, benzene emissions, Toluene, ambient emissions, fate and transport, catabolic enzyme induction, biodegradation, Methyl tert butyl ether, ethanol degradation, contaminant releaseProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.