INFLUENCE OF ETHANOL ON THE BIODEGRADATION AND TRANSPORT OF BTEX COMPOUNDS IN UNDISTURBED COLUMNS OF FINE-GRAINED MATERIAL

The use of methyl tert-butyl ether (MTBE) as a fuel oxygenate is currently being phased out with ethanol being the most likely replacement in most areas. Ethanol has been shown to have an influence on the biodegradation of petroleum hydrocarbons in the environment with the possibility of increased plume lengths. An experiment was conducted to determine the influence of ethanol on the biodegradation of benzene, toluene, ethylbenzene, and xylene (BTEX) in fine-grained material (loess) from northern Illinois. Three undisturbed columns (0.3 m in diameter by 0.4 m long) of loess were collected from approximately 1.7 to 2 m depth at an uncontaminated site at Northern Illinois University, DeKalb, Illinois. Uncontaminated groundwater was mixed with either BTEX or BTEX plus ethanol at concentrations that would be dissolved in groundwater as a result of a gasoline release. A third column was continuously fed uncontaminated groundwater. Effluent concentrations of BTEX were significantly higher in the ethanol-amended column than in the BTEX only column. Ethanol biodegradation lowered the pH, increased the conductivity, and altered the redox conditions compared to the two columns without ethanol. The biodegradation rates of benzene in the two experimental columns were determined to be 0.135 day-1 in the BTEX only column and 0.05 day-1 for the first 60 days in the ethanol-amended column. This is the first study to indicate that benzene was biodegraded in the presence of ethanol, but at a substantially lower rate than benzene without ethanol addition. This effect was only noted for the first 60 days of the experiment and by day 90 the biodegradation rates of benzene were similar in both columns as ethanol concentrations dropped to 1000 mg/L. Transport modeling using these biodegradation rates suggests a possible increase in benzene plume lengths between 34% and 68%. Given the major problems associated with the use of MTBE, ethanol, with its rapid biodegradation potential, appears to be a suitable substitute. However, the results of this and previous studies show that the addition of ethanol could pose a more serious threat of benzene contamination to groundwater supply wells.