A new pervaporation-biological oxidation hybrid process for the treatment of wastewaters containing volatile organic compounds (VOCs) has been investigated. The process combines pervaporation using a sweep gas with absorption and biological degradation of the permeate VOCs. A model system with monochlorobenzene (MCB) as the VOC and Pseudomonas JS150 as the degrading microorganism was used for the study. Relatively high temperatures for the pervaporation operation were used, allowing the use of lower membrane area and lower sweep gas flowrate. The resulting higher concentration of VOC in the sweep gas and the difference in temperatures between pervaporation unit and bioreactor, were expected to improve the mass transfer of VOC from the gas into the biomedium, leading to a better VOC removal from the gas stream. The performance of this system, working at a constant gas flowrate and a bioreactor temperature of 30 degreesC, was studied for step increases in pervaporation temperature. Raising the temperature was shown to increase the mass transfer flux in the membrane module. Bioreactor removal efficiencies close to 100% were obtained throughout, and an elimination capacity of 84 g (MCB) m(-3) h(-1) was attained. The system was then run with a lower bioreactor temperature (15 degreesC), in order to accurately quantify changes in removal efficiency with varying pervaporation temperature. In this case, a constant VOC load was fed to the bioreactor, with reductions in gas flowrates concomitant with increasing pervaporation temperatures. It was shown that using lower gas flowrates with higher VOC concentrations, at higher temperatures, resulted in significantly improved removal efficiencies. Concentrations of 17 g m(-3) of MCB1 were treated in the bioreactor working at 15 degreesC, with removals of 95%.