BACKGROUND: The integration of UV photocatalysis and biofiltration seems to be a promising combination of technologies for the removal of hydrophobic and poorly biodegradable air pollutants. The influence of pre-treatments based on UV254 nm photocatalysis and photo-oxidation on the biofiltration of toluene as a target compound was evaluated in a controlled long-term experimental study using different system configurations: a standalone biofilter, a combined UV photocatalytic reactor-biofilter, and a combined UV photo-oxidation reactor (without catalyst)-biofilter. RESULTS: Under the operational conditions used (residence time of 2.7 s and toluene concentrations 600-1200 mg C m(-3)), relatively low removal efficiencies (6-3%) were reached in the photocatalytic reactor and no degradation of toluene was found when the photo-oxidation reactor was operated without catalyst. A noticeable improvement in the performance of the biofilter combined with a photocatalytic reactor was observed, and the elimination capacity of the biological process increased by more than 12 g C h(-1) m(-3) at the inlet loads studied of 50-100 g C h(-1) m(-3). No positive effect on toluene removal was observed for the combination of UV photoreactor and biofilter. CONCLUSIONS: Biofilter pre-treatment based on UV(254) nm photocatalysis showed promising results for the removal of hydrophobic and recalcitrant air pollutants, providing synergistic improvement in the removal of toluene. (C) 2011 Society of Chemical Industry