Toluene degradation in the recycle liquid of biotrickling filters for air pollution control

Pollutant degradation in biotrickling filters for waste air treatment is ge nerally thought to occur only in the biofilm. In two experiments with tolue ne degrading biocrickling filters, we show that suspended microorganisms in the recycle liquid may substantially contribute to the overall pollutant r emoval. Two days after reactor start up, the overall toluene elimination ca pacity reached a maximum of 125 g m(-3) h(-1), which was twice that found d uring prolonged operation. High biodegradation activity in the recycle liqu id fully accounted for this short-term peak of pollutant elimination. Durin g steady-state operation, the toluene degradation in the recycle liquid was 21% of the overall elimination capacity, although the amount of suspended biomass was only 1% of the amount of immobilized biomass. The results sugge st that biotrickling filter performance may be improved by selecting operat ing conditions allowing for the development of an actively growing suspende d culture.