Biofiltration of high loads of ethyl acetate in the presence of toluene

To date, biofilters have been used primarily to control dilute, usually odo rous, off-gases with relatively low volatile organic compound (VOC) concent rations (<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 conce ntrations of VOCs and hazardous air pollutants (HAPs). In this study, the behavior of biofilters under high loads of binary VOC mi xtures was studied. Two bench scale biofilters were operated using a commer cially available medium and a mixture of wood chips and compost. Both were exposed to varying mixtures of ethyl acetate and toluene. Concentration pro files and the corresponding removal efficiencies as a function of VOC loadi ng were determined through frequent grab-sampling and GC analysis. Biofilte r response to two frequently encountered operating problems-media dry-out a nd operating temperatures exceeding 40 degrees C-was also evaluated under c ontrolled conditions. Microbial populations were also monitored to confirm the presence of organisms capable of degrading both major off-gas constitue nts. The results demonstrated several characteristics of biofilters operati ng under high VOC load conditions. Maximum elimination capacities for ethyl acetate were typically in the rang e of 200 g m(-3) hr(-1). Despite the presence of toluene degraders, the removal of toluene was inhib ited by high loads of ethyl acetate. Several byproducts, particularly ethanol, were formed. Short-term dry-out and temperature excursions resulted in reduced performan ce.