In this paper we present a review of the existing air pollution control technologies (APCT), when used essentially for the elimination of volatile organic compounds (VOC). The biotechnologies referred to, bioscrubbers, biotrickling filters and biofilters, are also described. A more detailed review of biofiltration is proposed, presenting the most recent and latest developments achieved in the field of bioprocessing. In particular, the influence of the filter bed, the polluted air flowrates, the pollutants, the pressure drop, bed moisture content, temperature, nutrients, pH and the microorganisms are reviewed. Models of biofiltration are also presented.

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The production of biogas in landfills, its composition and the problems resulting from its generation are all reviewed. Biofiltration is a promising option for the control of emissions to atmosphere of the methane contained in biogas issued from the smaller and/or older landfills. A detailed review of the methane biofiltration literature is presented. The microorganisms, mainly the methanotrophs, involved in the methane biodegradation process, and their needs in terms of oxygen and carbon dioxide utilization, are described. Moreover, the influence of nutrients such as copper, nitrogen and phosphorus, and the process operating conditions such as temperature, pH and moisture content of the biofilter bed, are also presented. Finally, the performance of various filter beds, in terms of their elimination capacities, is presented for laboratory scale biofilters and landfill covers.

The biofiltration process is a promising technology for the treatment of dilute styrene emissions in air (less than 1 g‚m -3 ). The efficiency of this process is however strongly dependent upon various operational parameters such as the filter bed characteristics, nutrient supplies, input contaminant concentrations, and gas flow rates (gas residence times). The biofiltration of air containing styrene vapors was therefore investigated, employing a novel biomass filter material, in two identical but separate laboratory scale biofiltration units (units 1 and 2), both biofilters being initially inoculated with a microbial consortium. Each biofilter was irrigated with a nutrient solution supplying nitrogen in one of two forms; i.e., mainly as ammonia for unit 1 and exclusively as nitrate for unit 2. The experimental results have revealed that greater styrene elimination rates (up to 141 g‚m -3 ‚h -1 ) are achieved in the biofilter supplied with ammonia as the major nitrogen source in comparison to the lesser elimination performance (up to 50 g‚m -3 ‚h -1 ) obtained with the nitrate provided biofilter. However, in achieving the high styrene removal rates in the ammonia supplied biofilter, the excess of biomass accumulates on the filtering pellets and causes progressive clogging of the filter media. Furthermore, the effectiveness of nitrate supply as the sole nitrogen nutrient form, on reducing or controlling the biomass accumulation in the filter media in comparison to ammonia, could not be satisfactorilly demonstrated because the two biofilters operated with very different styrene elimination capacities. The monitoring of the carbon dioxide concentration profile through both biofilters revealed that the ratio of carbon dioxide produced to the styrene removed was approximately 3/1, which confirms the complete biodegradation of removed styrene, given that some of the organic carbon consumed is also used for the microbial growth. The effects of the most important design parameters, namely styrene input concentrations and gas flow rates, were investigated for each nutrient solution.

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: Air bioÐltration is now under active consideration for the removal of the volatile organic compounds from air polluted streams. In order to investigate the performance of this newly developed technology, a bioÐltration pilot unit was operated for a continuous period of 8 months. The bioÐlter column was packed with commercially conditioned peat. At start-up, the Ðlter bed was inoculated with four species of microorganisms. The resulting bioÐlter was fed with air contaminated with toluene, xylene or a mixture of toluene and xylene. The maximum elimination capacities attained were 165 g m~3 h~1 for toluene, 66 g m~3 h~1 for xylene and 115 g m~3 h~1 for the mixture of toluene and xylene. These speciÐc performances exceed the values published in the technical and commercial literature for similar processes. Xylene isomers were degraded in decreasing order of reactivity, m-xylene, p-xylene, o-xylene. In the case of air polluted with a toluene and xylene mixture, it was noticed that the metabolism of toluene biodegradation was inhibited by the presence of xylene. Characterization of the bioÐlm microbial populations after several weeks of operation showed that the dominant strains among the isolated culturable strains from the bioÐlm, even if di †erent from the initially inoculated strains, had at least one physiological property favoring degradation of aromatic organic rings. The performance of the bioÐlter was found to be dependent on the temperature of the Ðlter media and the pressure drop through the bed. Finally, a steady state mathematical model was tested in order to theoretically describe the experimental results. This model is used to illustrate the operating di †usion and reaction regimes at steady state for the case of each pollutant.

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