The objective of this article is to define and biofilters are living pollution control systems and are validate a mathematical model that describes the physical subject to dynamic changes. This characteristic has hinand biological processes occurring in a trickle-bed air dered the widespread application of biofiltration in the biofilter for waste gas treatment. This model considers a United States, where regulatory requirements typically two-phase system, quasi-steady-state processes, unistipulate continuous compliance with emissions limitaform bacterial population, and one limiting substrate. The variation of the specific surface area with bacterial growth tions or destruction efficiency. To help develop biois included in the model, and its effect on the biofilter filtration as a viable technology capable of meeting performance is analyzed. This analysis leads to the conregulatory constraints, researchers have focused on unclusion that excessive accumulation of biomass in the derstanding the fundamental physical, chemical, and reactor has a negative effect on contaminant removal efficiency. To solve this problem, excess biomass is re-microbiological processes that control reactor performoved via full media fluidization and backwashing of the mance. biofilter. The backwashing technique is also incorporated Recently, biofilter models have been introduced that in the model as a process variable. Experimental data account for detailed representations of biofilm biodegfrom the biodegradation of toluene in a pilot system with radation mechanisms. Shareefdeen et al. (1993) profour packed-bed reactors are used to validate the model. Once the model is calibrated with the estimation of the posed a model for a single-component waste stream that unknown parameters of the system, it is used to simulate accounted for oxygen limitations in the biofilm. Smith the biofilter performance for different operating condi-(Smith, P. J. 1993. A fundamental approach to modeling tions. Model predictions are found to be in agreement the treatment of VOC laden exhaust gases in biofilters, with experimental data.