Vapor phase bioreactors (VPBs) have been accepted as a competitive alternative to the physoci-chemical treatment technologies and used for treatment of gaseous hydrocarbon and odors. Although a number of mathematical models were developed to aid in understanding the fate of pollutants, practitioners take little advantage of these tools. The primary reason for this is ascribed to the complexity of biofilm models.

  The primary objective of this study was to investigate removal of toluene, ethylbenzene, and/or p-xylene vapors in a compost-based biofilter under both steady state and transient conditions. A practical model was also developed and used to predict the performance of biofilter. Compost-based biofilters amended with adsorbing filter materials such as granular activated carbon (GAC) or tire powder were used in studying removal of toluene, ethylbenzene, and p-xylene vapors. Studies involved removal of each compound individually as well as in mixture with the others.

  The compost-based biofilter amended with GAC showed short acclimation period, stable performance, and higher removal efficiencies of VOC than the compost and compost/tire biofilters. Under transient conditions, the sorption capacity of filter materials tends to attenuate the changes in concentrations. Moisture content and nitrogen availability were the limiting factors for successful performance. The developed model was simple, but proved to be an effective tool to predict the removal efficiencies, elimination capacities, and depth-concentration profiles of each VOC under steady state concition. In addition, the model successfully explained the high sorptive capacity of filter materials containing GAC under transient condition. The removal of mixtures of toluene, ethylbenzene, and p-xylene vapors was studied in the compost/GAC biofilter. In toluene and ethylbenzene mixtures, the presence of toluene had a negligible effect on ethylbenzene removal, while the presence of ethylbenzene had a distint negative effect on toluene removal. Since monoaromatic hydrocarbons are biodegraded through same enzyme pathways, toluene and ethylbenzene may compete each other for degradation capacity within the biofilter. In toluene and p-xylene mixtures, the presence of toluene had a positive effect on p-xylene removal due to the co-metabolic effect of toluene, while the presence of p-xylene slightly reduced the degradation rates of toluene. According to the results from batch tests and biofilter tests, the ethylbenzene inhibitied the degradation of toluene much more than p-xylene inhibited the degradation of toluene.

  In toluene, ethylbenzene, and p-xylene mixtures, toluene removal was reduced by the presence of ethylbenzene and p-xylene. p-Xylene removal was enhanced due to positive substate interactions in TEX mixtures. Ethylbenzene was reduced, to a lesser extent, by the presence of other compounds. In TEX mixtures, the removal efficiencies were ranked ethylbenzene ≒ toluene ＞ p-xylene.

Keywords : adsorbing filter materials, biofiltration, ethylbenzene, granular activated carbon (GAC), p-xylene, tire powder, toluene