Biofiltration of High Loads of Ethyl Acetate in the Presence of Toluene

Abstract

To date, biofilters have been used primarily to control dilute, usually odorous, off-gases with relatively low volatile organic compound (VOC) concentrations (<1 g m -3 ) and VOC loads (<50 g m -3 hr -1 ). Recently, however, U.S. industry has shown an interest in applying biofilters to higher concentrations of VOCs and hazardous air pollutants (HAPs).In this study, the behavior of biofilters under high loads of binary VOC mixtures was studied. Two benchscale biofilters were operated using a commercially available medium and a mixture of wood chips and compost. Both were exposed to varying mixtures of ethyl acetate and toluene. Concentration profiles and the corresponding removal efficiencies as a function of VOC loading were determined through frequent grab-sampling and GC analysis. Biofilter response to two frequently encountered operating problems-media dry-out and operating temperatures exceeding 40 °C-was also evaluated under controlled conditions. Microbial populations were IMPLICATIONS To date, biofilters have been used primarily to control dilute, usually odorous, off-gases with relatively low VOC concentrations. Yet there is a growing interest in expanding to higher concentrations the range of suitable applications for biological waste air treatment. However, this type of application has a high rate of system failure. Impediments for this application were reported in two recent case studies in which the treatment of high loads of ethanol from a foundry and a bakery, respectively, resulted in reduced percentage removal of the contaminants, formation of odorous acetic acid, and problems maintaining the proper moisture content because of the exothermic nature of the biodegradation process. The present study reports bench-scale operation of biofilters under high VOC loading conditions of mixed pollutant and the factors that lead to these adverse operating states also monitored to confirm the presence of organisms capable of degrading both major off-gas constituents. The results demonstrated several characteristics of biofilters operating under high VOC load conditions.• Maximum elimination capacities for ethyl acetate were typically in the range of 200 g m -3 hr -1 .• Despite the presence of toluene degraders, the removal of toluene was inhibited by high loads of ethyl acetate.• Several byproducts, particularly ethanol, were formed.• Short-term dry-out and temperature excursions resulted in reduced performance. INTRODUCTIONIt is generally thought that biofilters are suitable only for the treatment of dilute emissions of odors, volatile organic compounds (VOCs) and hazardous air pollutants (HAPs). The large majority of biofilters installed to date treat off-gases containing organic carbon compounds at concentrations of less than 0.5 g m -3 . Corresponding VOC loads and elimination capacities rarely exceed 50 grams of organic carbon per cubic meter of biofilter material per hour (g m -3 hr). Recently, however, industrial users, particularly in the United States, and vendors of biofilters have been attr...

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