Background

The passage of the 1990 Amendments to the Clean Air Act significantly heightened the interest in reducing VOC (volatile organic compound) emission as a means of achieving identified overall air quality goals and required control of hydrocarbon emission. Anthropogenic sources of many VOCs, are numerous and results from the presence of VOCs in unburned gasoline, solvent evaporation, and industrial emissions. Most of the remaining VOC emissions are related to the processing, storage and use of liquid fuels and organic chemicals, to environmental remediation, and to wastewater treatment. Biological air pollution control devices convert pollutants to non-hazardous materials within the treated stream before its release to the environment, and generally employs oxidation. There are primarily three types of biological air pollution control devices employed by industry today: bioscrubbers, biofilters, and trickle bed air biofilters (TBAB). Bioscrubbers are two stage devices where absorption into water occurs in one column followed by aerobic biodegradation in an activated sludge tank. The water is continuously recirculated between the two stages. Excess biomass generated in the second is removed periodically. Bioscrubbers are efficient in degrading highly water soluble compounds. The second type of biological VOC control system is the biofilter. Biofilters use a natural organic medium composed of peat, compost, leaves, wood bark, and/or soil. The natural organic medium is impregnated with solid nutrients and buffers, and the bed moisture is maintained at a constant level by humidifying the air. The third type of biological air pollution control device is the TBAB, which utilizes synthetic media for microbial attachment.