During the past decade,biofiltration has increasingly been applied as an air pollution control technology to minimize or eliminate emissions of volatile organic compounds from industrial sources.Although of the ability of this technology to maintain high removal efficiency during relatively steady conditions has been well established for many waste streams,a limitation of this technology has been its inability to maintain high removal efficiency during transient periods of elevated contaminant loading(i.e.,"shock loading")typical of many industrial operations.Use of biofilter packing media containing an appreciable contaminant sorption capacity in combination with a sequencing batch operation strategy is a promising method for enhancing contaminant removal during both normal operation and shock loading events.In the research described herein,a conventional continuous-flow biofilter(CFB)and a sequencing batch biofilter(SBB)were operated for more than 295 days to treat a model waste gas stream containing a two-component mixture of toluene and methyl ethyl ketone(MEK).The CFB was packed with polyurethane foam cubes,while the SBB was packed with polyurethane foam cubes coated with activated carbon.During "normal" loading conditions,the model waste stream contained toluene concentrations ranging from 28 to 30 ppmv and MEK concentrations ranging from 80 to 89 ppmv.Both biofilters exhibited stable long-term performance with greater than 99% contaminant removal during these normal loading conditions.On a regular basis,the influent toluene and MEK concentrations were temporarily increased to five times the normal influent concentration for a duration of one hour to test performance during shock loading.Results demonstrate how SBB operation can increase contaminant removal during transient loading conditions.During transient loading experiments,the SBB was able to remove more than 99% of the influent contaminants when subjected to a loading a rate of 209 g center dot m~(-3)centre dot h~(-1).In comparison,the CFB exhibited lower overall removal efficiency.
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