Biofiltration is a versatile waste gas and odour treatment technology that has gained much acceptance in recent years to treat Volatile Organic Compounds (VOCs). A compost-based biofilter unit inoculated with a mixed microbial population was examined to treat toluene vapours from a synthetic and real gas stream. This biofilter was operated continuously for a period of 8 months at different flow rates, 0.024-0.144 m(3) h(-1), with toluene concentrations ranging up to 2.3 g m(-3). Removal efficiencies ranging from 40 to 95% and elimination capacities ranging from 3.5 to 128 g m(-3) h(-1) were observed depending on the initial loading rates. The dynamic behaviour of the biofilter was evident from the changes in the process conditions. The stability of the biomass was evident from the fast response of the biofilter to intermittent shut down and restart operations. The potential of the biofilter to handle industrial gas mixtures was proved with operation using a real sample from a pharmaceutical industry. Removal efficiencies of 60-90% for toluene and 60-80% for benzene from the gas mixture were achieved. (c) 2005 Elsevier Ltd. All rights reserved.