BACKGROUND: Biotrickling filtration is one of the most promising biotechnologies for off-gas treatment. However, gas-liquid mass transfer limitations constitute the most important drawback of biotrickling filters (BTFs) when treating hydrophobic pollutants. Oxygen limitations might also arise when treating soluble pollutants at high loading rates. In the present study, an easy-to-implement method for mass transfer characterization in BTFs based on dissolved oxygen measurements was investigated. RESULTS: k(L)a values for oxygen in the range 30-300 h(-1) were obtained by fitting the experimental data to a mathematical model with high correlation coefficients (average r(2) = 0.995). In addition, the k(L)a values for other gas pollutants of industrial and environmental interest (NH3, H2S, toluene and hexane) were estimated by means of an empirical correlation, which allowed calculation of their mass transfer rates in order to identify potential mass transfer limiting scenarios. CONCLUSIONS: The methodology proposed allowed for a rapid, easy and accurate determination of the k(L)a for oxygen under varied operational conditions, the mass transfer data obtained being in agreement with previous literature. The experimental k(L)a data obtained for oxygen and the methodology applied for the estimation of k(L)a for the target gaseous pollutants selected constitutes a valuable tool for the optimization, design and operation of BTFs. (C) 2013 Society of Chemical Industry