A new type of bioreactor for air pollution control has been developed. The new process relies on an organic-phase emulsion and actively growing pollutant-degrading microorganisms, made into a foam with the air being treated. This new reactor is referred to as a foamed emulsion bioreactor (FEBR). As there is no packing in the reactor, the FEBR is not subject to clogging. Mathematical modeling of the process and proof of concept using a laboratory prototype revealed that the foamed emulsion bioreactor greatly surpasses the performance of existing gas-phase bioreactors. Experimental results showed a toluene elimination capacity as high as 285 g(toluene) M 3 reactor h(-1) with a removal efficiency of 95% at a gas residence time of 15 s and a toluene inlet concentration of 1-1.3 g m(-3). Oxygen limited the reactor performance at toluene concentration above about 0.7-1.0 g m(-3); consequently, performance was significantly improved when pure oxygen was added to the contaminated air. The elimination capacity increased from 204 to 408 g m(-3) h(-1) with >77% toluene removal at toluene inlet concentrations of 2-2.2 g m(-3). Overall, the results show that the performance of the FEBR far exceeds that of currently used bioreactors for air pollution control. (C) 2003 Wiley Periodicals, Inc.