A novel trickling fibrous-bed bioreactor was developed for biofiltration to remove pollutants present in contaminated air. Air containing benzene as the sole carbon source was effectively treated with a coculture of Pseudomonas putida and Pseudomonas fluorescens immobilized in the trickling biofilter, which was wetted with a liquid medium containing only inorganic mineral salts. When the inlet benzene concentration (C-gi) was 0.37 g m(-3), the benzene removal efficiency in the biofilter was greater than 90% at an empty bed retention time (EBRT) of 8 min or a superficial air flow rate of 1.8 m(3) m(-2) h(-1). In general, the removal efficiency decreased but the elimination capacity of the biofilter increased with increasing the inlet benzene concentration and the air (feed) flow rate. It was also found that the removal efficiency decreased but the elimination capacity increased with an increase in the loading capacity, which is equal to the inlet concentration divided by EBRT. The maximum elimination capacity achieved in this study was similar to 11.5 g m(-3) h(-1) when the inlet benzene concentration was 1.7 g m(-3) and the superficial air flow rate was 3.62 m(3) m(-2) h(-1). A simple mathematical model based on the first-order reaction kinetics was developed to simulate the biofiltration performance. The apparent first order parameter K-1 in this model was found to be linearly related to the inlet benzene concentration (K-1 = 4.64 - 1.38 C-gi). The model can be used to predict the benzene removal efficiency and elimination capacity of the biofilter for benzene loading capacity up to similar to 30 g m(-3) h(-1). Using this model, the maximum elimination capacity for the biofilter was estimated to be 12.3 g m(-3) h(-1), and the critical loading capacity was found to be 14 g m(-3) h(-1). The biofilter had a fast response to process condition changes and was stable for long-term operation; no degeneration or clogging of the biofilter was encountered during the 3-month period studied. The biofilter also had a relatively low pressure drop of 750 Pa m(-1) at a high superficial air how rate of 7.21 m(3) m(-2) h(-1), indicating a good potential for further scale up for industrial applications.