Effect of the Gasoline Oxygenate Ethanol on the Migration and Natural Attenuation of BTEX Compounds in Contaminated AquifersEPA Grant Number: R828156
Title: 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: Lasat, Mitch
Project Period: June 1, 2000 through May 31, 2002 (Extended to January 31, 2004)
Project Amount: $194,878
RFA: Exploratory Research - Engineering, Chemistry, and Physics) (1999) RFA Text | Recipients Lists
Research Category: Water , Land and Waste Management , Air , Engineering and Environmental Chemistry
A likely upcoming replacement of methyl tertiary butyl ether (MTBE) with ethanol as a gasoline oxygenate represents attractive economic and environmental 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.
We seek to determine (1) if ethanol enhances BTEX migration in aquifers; (2) how ethanol affects catabolic enzyme induction 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.
We hypothesize that ethanol will decrease the tendency for BTEX to be retarded by sorption. This will increase BTEX migration velocities and plume length. Ethanol will also be easily biodegraded, which will accelerate oxygen depletion and result in larger anaerobic zones within the plume. Because benzene degrades very slowly (if at all) anaerobically, this will also contribute to longer benzene plumes. In addition, a high metabolic flux of ethanol (when present at relatively high concentrations) will repress the synthesis of BTEX-degrading enzymes. This will result in the preferential degradation of ethanol. Nevertheless, simultaneous degradation of ethanol and BTEX will occur at low substrate concentrations.
Aquifer columns, experiencing transitions in electron acceptor conditions that mimic contaminated sites, will be fed water spiked with regular or ethanol-amended gasoline to discern the effect of ethanol on the fate and transport of individual BTEX compounds. Concentration profiles along the column length will be used to determine how ethanol affects BTEX degradation rates under different electron acceptor conditions, and treatment end points. Column samples will be analyzed with MPN techniques to determine how the concentration of BTEX degraders changes through these geochemical transitions. Chemostats seeded with P. putida F1 will be used to determine the concentration-dependent effect that ethanol may have on the expression of toluene dioxygenase, a model enzyme that degrades BTEX. These experiments will be complemented with microcosm assays to further delineate the conditions leading to a simultaneous versus sequential degradation of BTEX/ethanol mixtures.
This project will enhance the adaptation of current risk assessment and remediation approaches to the increasing possibility of encountering ethanol in BTEX plumes. Determining the effect of ethanol on BTEX retardation factors and degradation kinetics under different electron acceptor conditions will help formulate more accurate fate and transport models. In addition, biodegradation of contaminant mixtures is not well understood at the biochemical level. Thus, the chemostat experiments will provide valuable insight into the regulation of contaminant-specific enzyme activity as a function of the metabolic flux of alternative substrates.