Biofiltration of Odorous Gases

Abstract

Biofiltration is an emerging and attractive air pollution control technology for controlling odors, volatile organic carbons (VOCs), and air toxics. It has numerous advantages over conventional air pollution control methods. Biofiltration units are microbial systems incorporating microorganisms grown on a porous solid media such as compost, peat, soil, or a mixture of these materials. The filter media and the microbial culture are surrounded by a thin film of water called biofilm. Waste gases containing biodegradable VOCs and inorganic air toxics are vented through this material, where soluble contaminants partition into the liquid film and are biodegraded by the microorganisms in the biofilm. The technology has been applied to a wide range of industrial and public sector sources for the abatement of odors, VOCs and air toxics, with removal efficiency of more than 90%. Because of its economic benefit over the traditional air pollution control alternatives coupled with environmental advantages, biofiltration is becoming more popular in meeting the statutory emission regulations. Biofiltration harnesses the natural degrading abilities of microorganisms to biochemically oxidize waste gas contaminants into environmentally benign end products such as carbon dioxide, water, and mineral salts. Conventional air pollution control technologies such as carbon adsorption, incineration, etc., can treat a wide variety of pollutants at higher concentrations, however, for treating waste air with low pollutant concentrations these approaches become economically prohibitive. In comparison, biofiltration is more cost-effective particularly for treatment of large volumes of waste air with low concentrations of biodegradable contaminants. The low cost of biofiltration is associated with its use of natural sorbents and microbial oxidation. However, one must accept the trade-off in terms of longer residence time that is partially compensated by lower operating cost. The acceptance of biofiltration has followed from advances in biotechnology that provide thorough knowledge about the system and how the process can be optimized, not only to achieve high removal efficiencies with low energy consumption, but to achieve these elimination efficiencies over long periods with minimal maintenance. Further research is needed to develop good understanding of the metabolic degradation pathways for single and multiple contaminant waste gas streams, effective mass transfer from gas to liquid phase, and improved modeling techniques incorporating better kinetic data.