Characterization of a Flax Fiber Laboratory-Scale Biofilter Degrading Buthyl Acetate

In a pilot scale biofilter system, a new flax fiber packing material was used as a biofilter material. The waste gas was generated by injecting buthyl acetate to the inlet air stream by aid of a peristaltic pump. The waste air stream was humidified in a scrubber column before entering the biofilter, to create and maintain moisture in the biofilter. The flax fiber structure was inoculated with preselected microorganisms capable of degrading buthyl acetate. The microorganisms originated from a wastewater treatment plant and had been selected with buthyl acetate as the sole carbon source in shake flasks for 6 months prior to inoculation. The biofilter experiments were performed over a period of 8 weeks. Buthyl acetate concentrations in the gas phase have been maintained in the range of 160-620 mg/m3 and the flow rates have varied from 0,20 to 0,72 m3/min. The biofilter experiments were performed as factorial experiments at two levels with reference to the waste air flow and the solvent concentration. The maximum elimination capacity was around 60 %, which is low compared to compost based biofilter materials. The results from the factorial experiments show that the the flow had more effect on the degrading capacity than the concentration within the intervals investigated. These results were in accordance with sorption experiments performed, which showed that the sorption capacity of the flax fiber packing material was limited. The air flow characteristics have been studied by measuring the retention time and the degradation capacity in different parts of the biofilter. The results showed that channeling effects occurred in the biofilter and that the degradation capacity varied in different parts of the biofilter. The pressure drop over the biofilter was very low, about 1 mm WP. The moisture content was difficult to analyse since the packing material was constructed as a rigid homogenous structure, in which sampling was difficult to achieve without destroying the material. The moisture tests performed, showed a moisture content around 60 weight % water. The filter material needs improvement regarding mechanical properties, since the packing material decreased in volume by 20 % during 8 weeks of experimentation. Another proposed improvement is to increase the biofilter material density. The surface area for sorption and for biological growth would increase and thus the volumetric capacity of the biofilter

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