Biological methods, including biofiltration, have been used to treat the air from odoriferous volatile organic compounds (VOCs) for many years, mainly due to low operating costs and very low waste. An interesting mode of biofiltration realization is the use of biotrickling filters. Biotrickling filters enable the most complete control and regulation as well as stability of the process, even for harsh process disturbances (lack of gas flow or a sudden inlet load increase), as comparing to other bioreactors intended for biofiltration (conventional biofilters, bioscrubbers). Despite the mentioned advantages, the removal of hydrophobic volatile organic compounds from air in biotrickling filters is significantly lower than for hydrophilic compounds, mainly due to mass transfer limitation from the gas to biofilm phase. In order to increase the removal efficiency of such compounds, various solutions are proposed, e.g. the addition of surface-active substances or the use of pre-treatment (UV radiation). Recent literature reports, including own research indicate that improving the effectiveness of hydrophobic compounds removal in biotrickling filter can be obtained by introducing hydrophilic compounds into the gas stream. Such a solution is close to real systems, where the streams of polluted gases usually contain mixtures of VOCs or where it is possible to combine gas streams with either hydrophobic or hydrophilic predominating compounds. However, the mechanism of synergetic action of hydrophilic VOC during the treatment of hydrophobic VOCs is not defined due to poor available experimental data in this respect. In addition, the results of experimental investigations of biotrickling filtration concern almost exclusively biological systems based on bacteria, while much higher efficiency of VOCs removal, especially hydrophobic VOCs, is obtained in mixed consortia using fungi. It is of special importance because fungi have an aerial mycelium increasing the solid/liquid – gas interfacial area as well as containing hydrophobins playing a crucial role during the growth and development of filamentous fungi, resulting in efficient attachment of the hydrophobic compounds. The main aim of this project is to elucidate the mechanisms of enhanced removal of hydrophobic compounds (hexane, cyclohexane, toluene) in the presence of hydrophilic ethanol. Investigations will be performed in a polyurethane foam packed biotrickling filter inoculated with a defined fungal consortium.