ETHANOL AND BTEX BIODEGRADATION IN A POROUS POT REACTOR BY A MIXED CULTURE

Ethanol (EtOH) is a gasoline additive used to improve air quality by reducing emissions and is being considered as a replacement for methyl tert-butyl ether (MTBE). Benzene, toluene, ethylbenzene, and xylene (BTEX) are other gasoline components that can leak into groundwater supplies from underground storage tanks. Because of the potential adverse health effects of BTEX, the impact that ethanol has on the degradation of BTEX is currently being investigated. This study investigates the aerobic biodegradation of BTEX in the presence of ethanol under continuous feed conditions using a bacterial enrichment culture. A continuous flow stirred tank reactor with a biomass retention system (porous pot) was found to degrade both BTEX and ethanol simultaneously to achieve greater than 99.99% removal of the contaminants. The reactor was operated at decreasing hydraulic retention times (HRTs) to evaluate performance in conditions more applicable to full-scale applications. At HRTs of 4.3, 3.3, and 1.5 days, the effluent concentrations of ethanol and BTEX in the reactor were consistently below 1 μg/L. When the HRT was reduced to below 1.5 days, the biomass began to clog the reactor. It became necessary to regularly change the porous pot and begin wasting biomass for operation to continue. During these periods of operation, the effluent concentrations of ethanol and BTEX rose above 0.001 mg/L, but remained below the maximum contaminant levels for drinking water. Denaturing Gradient Gel Electrophoresis (DGGE) analysis monitored the composition of the culture at various stages of operation. Throughout operation, the culture was continuously in transition. The changing and diverse microbial community shows the wide variety of organisms capable of degrading ethanol and BTEX.