Effect of ethanol and biodiesel addition on the movement and biodegradation of volatile petroleum hydrocarbons in the subsurface

Abstract

The microbial degradation of typical volatile petroleum hydrocarbons in an aerobic sandy soil was studied with and without the blending of 10 percent ethanol (E10) or 20 percent biodiesel (B20) in batch microcosms and minilysimeters. In the head-space of the mini-lysimeters all volatile compounds remained above the analytical detection limits over 92 days except toluene in the pure petroleum hydrocarbon mixture (PP) and ethanol in E10. The mass percentage of each petroleum hydrocarbon compound remaining at the end of the experiments was comparable for all fuel mixtures, except for m-xylene, which was significantly less reduced in E10 as compared to PP and B20. Total cell counts at the end of the experiments were highest for E10 and lowest for PP. DGGE analysis revealed a distinct microbial community structure for each fuel mixture. Batch studies confirmed these observations, in particular slower degradation of toluene in the presence of ethanol. Inorganic nutrient addition to the batch systems resulted in higher total cell counts, more rapid microbial degradation rates and more similar microbial community structures. Under aerobic conditions, competition for scare inorganic nutrients seems to be the most plausible reason for slower monoaromatic hydrocarbon biodegradation in the presence of more readily degradable biofuel.