THE EFFECTS OF ETHANOL ON BTEX NATURAL ATTENUATION (PURE CULTURE
AND AQUIFER COLUMN EXPERIMENTS)
1
Marcio Luis Busi da Silva, 2Nanh Lovanh, 3Craig S. Hunt, and 3Pedro J.J. Alvarez
1,2,3
Department of Civil and Environmental Engineering, 2130 SC, University of Iowa, Iowa City,
IA 52242; 1Phone: (319) 335-5054; 1E-mail: msilva@engineering.uiowa.edu; 2E-mail: nanhlovanh@uiowa.edu.
Although considerable progress has been made toward understanding hydrogeochemical
factors that affect BTEX migration and biodegradation, little attention has been given to how
differences in gasoline formulation affect natural attenuation processes. In this regard, the use of
ethanol as a gasoline additive is increasing worldwide, both as a substitute fuel for imported oil
and as an oxygenate to minimize air pollution from combustion. Yet, little is known about the
effect of ethanol on biodegradation and migration of the toxic BTEX contaminants.
In this work, chemostat experiments were performed to investigate the effect of ethanol
on aerobic benzene degradation, and to delineate the conditions that lead to simultaneous versus
preferential biodegradation of ethanol when BTEX compounds are present. Chemostats were
seeded with Pseudomonas putida F1 (PpF1), and fed benzene and ethanol. The influent benzene
concentration was about 1 mg/L, and the dilution rate was 0.25 h-1. The addition of ethanol to the
influent at a concentration with equal chemical oxygen demand (COD) to the added benzene
resulted in a 70% decrease in the steady-state effluent benzene concentration. This effect was
representative of results with carbon-limiting conditions, and was attributed to an ethanolsupported increase in biomass, resulting in faster benzene degradation rates. When ethanol was
added to the influent at a high enough concentration that oxygen became limiting, no significant
benzene degradation occurred. This suggests that simultaneous degradation is the normal mode
of multiple substrate degradation when carbon is limiting, and preferential degradation would
occur when carbon is not limiting.
Additional research of the effect of ethanol on BTEX bioremediation is being conducted.
Aquifer columns have been constructed to study both the biotic and abiotic effects of ethanol on
natural attenuation of gasoline releases. The column is of a large enough size (120 cm length by
5 cm diameter) and the hydraulic residence time is long enough (~7 days) for anaerobic zones to
develop. One hypothesis for this work is that ethanol will be preferentially degraded under both
aerobic and anaerobic conditions, extending the time and distance required for BTEX
concentrations to be attenuated below regulatory limits. Theoretical considerations and
preliminary results also indicate ethanol could increase BTEX migration velocities by decreasing
sorption-related retardation during transport.
In conclusion, the use of ethanol as a gasoline oxygenate represents potential economic
and air-quality benefits. Nevertheless, the inhibition of BTEX biodegradation and the possible
decrease in sorption-related retardation suggests that ethanol is likely to increase BTEX plume
lengths. The net effect of ethanol on natural attenuation of BTEX is likely to be system specific,
depending largely on the release scenario and the assimilative capacity of the aquifer.
Key words: natural attenuation, ethanol, MTBE, BTEX