BACKGROUND: A two-stage bioreactor, comprising a biotrickling filter (BTF) as the first stage and a biofilter (BF) as the second stage, operated under steady- and transient-state conditions, was tested to remove gas-phase hydrogen sulphide, methanol and alpha-pinene. RESULTS: Hydrogen sulphide and methanol were removed in the first stage, while alpha-pinene, was removed predominantly in the second-stage fungal BF. The effect of the liquid trickling rate was evaluated in the BTF, while concentration-dependent synergistic and antagonistic interactions in both reactors were assessed by varying the concentration of one pollutant, and by maintaining 100% removal of other pollutants. Increasing the liquid trickling rate decreased methanol removal significantly, from >93% to 40%. Increasing the concentration of hydrogen sulphide from low to high loading rates did not affect the removal of volatile organic compounds (VOCs), however, the reverse occurred. Under all the conditions tested, alpha-pinene removal in the second-stage biofilter still remained higher than 80%. CONCLUSIONS: The results show the maximum elimination capacities achievable for this complex ternary mixture, under a wide range of operating conditions. (C) 2010 Society of Chemical Industry