IntroductionIndustrial gas-phase emissions of hazardous contaminants Ž . including volatile organic compounds VOCs are widely regarded as risks to environmental and occupational health. A broad spectrum of innovative treatment technologies are currently available for the control of such industrial emissions, among which biofiltration is a viable alternative. The biofiltration process involves the growth of heterotrophic microorganisms immobilized on a solid surface and sustained by the organic components of the gas stream. The technology has several advantages over traditional physical or chemical processes such as thermal destruction, carbon adsorption, and liquid scrubbing; and these include low energy consumption, and, consequently, low operating and maintenance costs. Ž . Furthermore, granular activated carbon GAC employed as a biofilter packing material not only provides a favorable environment for biofilm growth, but also extends the contact time between the biofilm and contaminants due to its desirCorrespondence concerning this article should be addressed to M. Pirbazari. Current address of W. Den: Dept. of Environmental Science, Tunghai University, Tai-Chung, Taiwan. able adsorptive characteristics. These beneficial features attributed to the adsorptive characteristics of GAC and biodegradative ability of the biofilm are particularly important in the degradation of recalcitrant compounds. These aspects have been well addressed by several researchers in both Ž aqueous-phase systems Ying and Weber, 1979; Kim and Pir-. bazari, 1989; Ravindran et al., 1997 and in gas-phase systems Ž . De heyder et al., 1994; Man et al., 1996 . An important aspect regarding implementation of full-scale biofiltration systems is their economic planning and design. A modeling and design protocol may indeed be a valuable tool to minimize the scope of elaborate, time-consuming, and expensive pilot-scale testing normally considered before a fullscale design is contemplated upon. Therefore, the present study focuses on the development of a mathematical modeling technique for performance prediction and simulation of biofilters under various operating conditions. The proposed model has the versatility of using either adsorbing or nonadsorbing media. The study is also intended to establish a systematic approach in determining the model input parameters, and to verify the predictive capability of the model. In the present study, GAC was employed as the biofilter packSeptember 2002 Vol. 48, No. 9AIChE Journal 2084 Ž . ing medium, and trichloroethylene TCE was chosen as the model compound.