Biofiltration of air contaminated with toluene on a compost-based bed

Many studies have focused on problems created by emissions to the atmosphere of gaseous effluents containing volatile organic compounds (VOCs). Over the more recent decades, such studies have led to the development of various bioreactors such as the bioscrubber, the biotrickling filter and the biofilter. This paper presents the results of a study on the biofiltration of airborne toluene, the biofilter employed being operated at the laboratory-scale for a continuous period of 3 months. The focus of this particular study has been the development of a new compost-based filter-bed material, which consists of an association between matured compost and a proprietary organic binder that is intended to prolong the period of the bed's efficient operations. No inoculum was added to the filter-bed material. During the experimental program, the performance of two different bed irrigation solutions was examined, the most effective nutrient supply solution then being used, along with toluene input levels varying from 0.6–2.6 g/m3, and toluene polluted air flow rates ranging from 0.4–1 m3/h, equivalent to empty bed residence times of 65–165 s. The results of this program have demonstrated removal efficiencies approaching 95%, while maximum elimination capacities of 55 g/m3 h, for an inlet load of 65 g/m3 h, have been achieved, supporting the view that the compost-based filter material tested in this work functions as a promising biofilter medium in this application. Finally, in order to present the biofilter performance observed under the best operating conditions, a simplified representation based on Ottengraf's model has been developed from the experimental results and is included here.