Field-scale biofiltration: Performance evaluation and microbial analysis

Abstract

Biofiltration has been shown to be an effective method for the remediation of volatile organic compounds (VOC's), particularly petroleum vapors extracted from the vadose zone. Many bacteria have the enzymatic pathways necessary for aerobic mineralization of VOC's to form cell biomass, carbon dioxide and water. Molecular methods such as nucleic acid hybridizations and the polymerase chain reaction (PCR), are methods that can be applied to environmental samples to characterize bacterial community structure and function. The research presented here reports the use of a field-scale biofilter for the remediation of unleaded gasoline vapors extracted from the vadose zone. An evaluation of contaminant removal efficiency over a five month period showed that the biofilter removed 90% of total petroleum hydrocarbons and greater than 90% of the EPA priority pollutants benzene, toluene, ethylbenzene, and xylene. The bacterial consortium in the biofilter medium readily adapted to increased loading rates, and variations in temperature and moisture. A combination of conventional cultural and molecular methods was used to track the bacterial populations over the course of the experiment. Polymerase chain reaction amplification of the small ribosomal subunit DNA sequence was used for identification of bacterial isolates and the design of DNA hybridization probes. Hybridization of these probes to community DNA samples taken from the biofilter over time revealed changes in specific bacterial populations as bioremediation occurred. Specifically, bacteria that could use gasoline, toluene, ethylbenzene or xylene were prevalent throughout the biofilter. Bacterial populations that could degrade xylene gradually increased over time, while overall total population size was the similar in the background sample and at the end of the study.