BACKGROUNDGas-liquid mass transfer still constitutes an important constraint for hydrophobic volatile organic compound (VOC) removal in biotrickling filters (BTFs), packing material and liquid recirculation rate being two key parameters governing this mass transfer. The combined impact of both parameters on the abatement of VOCs has not been yet assessed. This work evaluated the influence of the trickling liquid velocity on process performance under two packed bed configurations (random vs. structured) in a BTF treating toluene and ethylbenzene. RESULTSSimilar removal efficiencies >90% for both toluene and ethylbenzene (corresponding to elimination capacities of approximate to 50 and 32 g m(-3) h(-1), respectively) were achieved regardless of the configuration. However, less intensive operating conditions were applied in the structured BTF compared to those implemented in the random packed-bed BTF (optimal trickling liquid velocities of 10 and 20 m h(-1) and liquid renewal rates of 400 and 800 mL d(-1), respectively). CONCLUSIONThe superior performance of the structured monolith packing at milder operating conditions was attributed to an improved liquid distribution and the reduction of dead volumes and preferential gas flow channels. Proper selection of the packing material would result in an important reduction in both energy and fresh water consumption. (c) 2018 Society of Chemical Industry