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Final 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: Krishnan, Bala S.
Project Period: June 1, 2000 through May 31, 2002 (Extended to January 31, 2004)
Project Amount: $194,878
RFA: Exploratory Research - Environmental Engineering (1999)
Research Category: Engineering and Environmental Chemistry
Description:
Objective:A likely upcoming replacement of methyl tertiary-butyl ether with ethanol as a gasoline oxygenate represents attractive economic and air-quality benefits. Fuel releases that contaminate the subsurface, however, likely are to continue well into the future. Thus, a basic understanding of how ethanol affects the fate and transport of benzene, toluene, ethylbenzene, and xylenes (BTEX) in aquifers (and related remediation activities) is needed before a widespread changeover occurs.
The objectives of this research project were to: (1) evaluate the feasibility of enhancing the natural attenuation of BTEX-ethanol releases through anaerobic bioaugmentation using acclimated methanogenic enrichments; (2) develop a real-time quantitative polymerase chain reaction (RT-qPCR) method to detect and quantify bacteria that can degrade benzene under strongly anaerobic conditions; and (3) develop a mathematical model to characterize the effect of ethanol on the fate and transport of BTEX compounds in groundwater aquifers.
Summary/Accomplishments (Outputs/Outcomes):Objective 1. Evaluate the Feasibility of Enhancing the Natural Attenuation of BTEX-Ethanol Releases Through Anaerobic Bioaugmentation Using Acclimated Methanogenic Enrichments
Methanogenic flowthrough aquifer columns were used to investigate the potential of bioaugmentation to enhance anaerobic BTEX degradation in groundwater contaminated with ethanol-blended gasoline. Two different methanogenic consortia (enriched with benzene or toluene and ο-xylene) were used as inocula. Toluene was the only hydrocarbon degraded within 3 years in columns that were not bioaugmented, although anaerobic toluene degradation was observed after only 2 years of acclimation. Significant benzene biodegradation (up to 88%) was observed only in a column bioaugmented with the benzene-enriched methanogenic consortium. This removal efficiency was sustained for 1 year with no significant decrease in permeability resulting from bioaugmentation. Benzene removal was hindered by the presence of toluene, which is a more labile substrate under anaerobic conditions. RT-qPCR analysis showed that the highest numbers of bssA gene copies (coding for benzylsuccinate synthase) occurred in aquifer samples exhibiting the highest rate of toluene degradation, which suggests that this gene could be a useful biomarker for environmental forensic analysis of anaerobic toluene bioremediation potential. bssA continued to be detected in the columns 1 year after column feeding ceased, indicating the robustness of the added catabolic potential. Overall, these results suggest that anaerobic bioaugmentation might enhance the natural attenuation of BTEX in groundwater contaminated with ethanol-blended gasoline, although field trials would be needed to demonstrate its feasibility. This approach may be especially attractive for removing benzene, which is the most toxic and commonly the most persistent BTEX compound under anaerobic conditions.
Objective 2. Develop a RT-qPCR Method To Detect and Quantify Bacteria That Can Degrade Benzene Under Strongly Anaerobic Conditions
Benzene is a common groundwater pollutant that often is recalcitrant under the anaerobic conditions that prevail at hydrocarbon-contaminated aquifers. Thus, determining the potential for anaerobic benzene degradation is important to assess the feasibility of intrinsic bioremediation. In this work, we developed a 16S rDNA biomarker to estimate the concentration of putative benzene degraders in a benzene-degrading methanogenic consortium that has been enriched on benzene for several years. Primers were designed based on phylogenetic information obtained by sequencing selected denaturing gradient gel electrophoresis bands from this consortium. The primers and probe that corresponded to Desulfobacterium sp. (the dominant band) showed amplification with DNA from the benzene-enriched methanogenic culture but not with DNA samples from negative controls (i.e., toluene-degrading and dehalorespiring methanogenic consortia that do not degrade benzene). Samples from an anaerobic aquifer column that was bioaugmented with the benzene-degrading consortium 3 years ago showed a strong correlation between benzene degradation activity and the concentration of putative benzene degraders. This is the first report of the use of RT-qPCR for forensic analysis of anaerobic benzene degradation. Further research is need to determine if this biomarker will be broadly applicable to assess benzene degradation potential under strongly anaerobic (sulfate reducing and methanogenic) conditions.
Objective 3. Develop a Mathematical Model To Characterize the Effect of Ethanol on the Fate and Transport of BTEX Compounds in Groundwater Aquifers
An ancillary objective of this project was to develop a mathematical model to evaluate how ethanol affects the fate and transport of BTEX compounds in groundwater aquifers. A commonly used numerical model (RT3D) was setup to incorporate substrate interactions, such as metabolic flux dilution and catabolite repression exerted by ethanol, as well as its positive effects on enhanced microbial growth (including benzene degraders). The model also considers the geochemical footprint of ethanol degradation, such as the depletion of electron acceptors. A custom reaction module for RT3D was developed in cooperation with Groundwater Services, Inc. to consider sequential depletion of electron acceptors during ethanol degradation, the dilution of BTEX metabolic flux, and catabolite repression. Cosolvency effects influencing sorption-related retardation were analyzed theoretically but not included in the model because such effects are expected to be negligible at the ethanol concentrations expected at sites contaminated by ethanol-amended gasoline (< 10,000 mg/L). The model was calibrated and validated using the Keesler Air Force Base case and field data from the BIOSCREEN user’s manual. Simulations were in excellent agreement with the observed values (R2 of 0.976). Four scenarios were tested for benzene degradation, showing all the inhibitory processes. Simulations suggest that the most important plume-elongation process is catabolite repression, followed by metabolic flux dilution, and finally, depletion of oxygen during ethanol consumption. Simulations with ethanol show a significant enlargement of the benzene plume length (23%). These values closely matched field and statistical studies from the literature. Overall, this model holds great potential to evaluate the influence of different substrate interactions between ethanol or other gasoline additives and BTEX compounds on the fate and transport of such releases.
This project also subsidized part of an ongoing Ph.D. dissertation (Mr. Diego E. Gomez, “Development of a mathematical model to characterize the effect of ethanol on the fate and transport of BTEX compounds in groundwater aquifers”) and the postdoctoral training of Dr. Marcio L.B. da Silva. Hence, directly and indirectly, this project has contributed to improvements in the nation’s scientific and engineering research, education, and human resource base.
Journal Articles on this Report: 10 Displayed | Download in RIS Format
| Other project views: | All 34 publications | 13 publications in selected types | All 10 journal articles |
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Beller HR, Kane SR, Legler TC, Alvarez PJJ. A real-time polymerase chain reaction method for monitoring anaerobic, hydrotarbon-degrading bacteria based on a catabolic gene. Environmental Science & Technology 2002;36(18):3977-3984. |
R828156 (Final) |
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Lovanh N, Alvarez PJJ. Effect of ethanol, acetate, and phenol on toluene degradation activity and tod-lux expression in Pseudomonas putida TOD102: Evaluation of the metabolic flux dilution model. Biotechnology and Bioengineering 2004;86(7):801-808. |
R828156 (Final) |
not available |
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Ruiz-Aguilar GM, Fernandez-Sanchez JM, Kane SR, Kim D, Alverez PJJ. Effect of ethanol and methyl-tert-butyl ether on monoaromatic hydrocarbon biodegradation: Response variability for different aquifer materials under various electron-accepting conditions. Environmental Toxicology and Chemistry 2002;21(12):2631-2639. |
R828156 (Final) |
not available |
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Lovanh N, Hunt CS, Alvarez PJJ. Effect of ethanol on BTEX biodegradation kinetics: aerobic continuous culture experiments. Water Research 2002;36(15):3739-3746. |
R828156 (Final) |
not available |
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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) |
not available |
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Deeb RA, Sharp JO, Stocking A, McDonald S, West KA, Laugier M, Alvarez PJJ, Kavanaugh MC, Alvarez-Cohen L. Impact of ethanol on benzene plume lengths: microbial and modeling studies. Journal of Environmental Engineering-ASCE 2002;128(9):868-875. |
R828156 (Final) |
not available |
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Ruiz-Aguilar GML, O'Reilly K, Alvarez PJJ. A comparison of benzene and toluene plume lengths for sites contaminated with regular vs. ethanol-amended gasoline. Ground Water Monitoring and Remediation 2003;23(1):48-53. |
R828156 (Final) |
not available |
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Da Silva MLB, Alvarez PJJ. Enhanced anaerobic biodegradation of benzene-toluene-ethylbenzene-xylene-ethanol mixtures in bioaugmented aquifer columns. Applied and Environmental Microbiology 2004;70(8):4720-4726. |
R828156 (Final) |
not available |
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Fang JS, Lovanh N, Alvarez PJJ. The use of isotopic and lipid toluene degradation to specific analysis techniques linking microorganisms: applications and limitations. Water Research 2004;38(10):2529-2536. |
R828156 (Final) |
not available |
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Da Silva MLB, Ruiz-Aguilar GML, Alvarez PJJ. Enhanced anaerobic biodegradation of BTEX-ethanol mixtures in aquifer columns amended with sulfate, chelated ferric iron or nitrate. Biodegradation 2005;16(2):105-114. |
R828156 (Final) |
not available |
ethanol, gasoline oxygenate, ethanol-blended gasoline, economic benefits, air-quality benefits, benzene, toluene, ethylbenzene, xylenes, BTEX, anaerobic bioaugmentation, bacteria, bioaugmentation, groundwater,
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Toxics, Air, Scientific Discipline, Waste, RFA, chemical mixtures, Remediation, Engineering, Chemistry, & Physics, EPCRA, HAPS, Environmental Chemistry, 33/50, Bioremediation, risk assessment, gasoline, ethanol degradation rates, electron accpter conditions, biodegradation, fate and transport, ambient emissions, BTEX migration, benzene, Methyl tert butyl ether, MTBE, air sampling, benzene emissions, biological attenuation, contaminated aquifers, contaminant release, electron acceptor, Toluene, catabolic enzyme induction, ethanol degradation, Benzene (including benzene from gasoline)
Progress and Final Reports:
2001 Progress Report
Original Abstract