The treatment of air pollutants in a biofilter requires that the compound to be degraded be effectively transported from the gas to the organisms which reside in a biofilm that forms upon the packing material. Conventional models of biofilters treat these biofilms as if they are water and so predictions based on such models indicate that water insoluble compounds should have very poor removal rates. While it is generally true that biofilter efficiency declines with water solubility, models based on the biofilm behaving like water predict negligible removal for very insoluble compounds such as alpha-pinene (solubility approximately 2 mg/L). However, recent research shows relatively high removal rates for alpha-pinene, an important pollutant in many forest products emissions. The hypothesis of this research is that the transport properties of a biofilm treating hydrophobic pollutants are significantly different from those of water. This affects the biofiltration of hydrophobic compounds, resulting in considerably greater removal of these compounds than predicted based on air/water partition coefficients and diffusion coefficients through water. Moreover, it is hypothesized that the transport rates are compound specific and may depend on the compound used by the biofilm. A diffusion cell has been designed and built to study the partitioning from air and diffusion of alpha-pinene through various natural and artificial biofilms. Based on the solution of the pseudo-steady state mass balance between the two chambers, a semi-log plot can be used to determine the ratio of the diffusivity of a compound through a particular film to the air/film partition coefficient. The average diffusion coefficient through agar, which has the same partitioning properties as water, was found to be 3.4 x 10~(-6)cm~2/s (S.D.: 1.2 x 10~(-6)cm~2/s, n=12). This is on the same order of magnitude as the value of 6.3 x 10~(-6)cm~2/s for water calculated using the Wilke-Chang correlation for free solutions. Diffusion cell experiments were performed with alpha-pinene using inactivated biofilm, previously grown on methanol and alpha-pinene, immobilized in agar. The results with the methanol biofilm indicate that initially sorption takes place within the film but once a pseudo-steady state has been reached, the ratio of the diffusion coefficient to the partition coefficient of the mobile phase is not significantly different from the agar experiments.
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