Removal of hydrophobic volatile organic compounds from the air in biofiltration processes is much less effective than in the case of hydrophilic compounds. This is mainly due to the limited solubility of hydrophobic compounds in water as well as their resistance to biodegradation. In order to improve the removal of hydrophobic compounds in biotrickling filters, following approaches are practiced: modification of the liquid with surfactants, addition of a water-immiscible organic phase (mainly silicone oil) or mixing gas streams containing both hydrophobic and hydrophilic components. The research results available in the literature suggest that the most promising solution of the above-mentioned is the use of two-phase/two-component trickling liquid systems. Despite the recently observed increase in interest in the use of the so-called deep eutectic solvents (DES), successfully applied for the absorption of pollutants from water and air, there are no studies on the use of such liquids in the biofiltration process. Features of DES compounds obtained from natural materials, i.e. non-toxicity, low volatility, hydrophobic properties, the possibility of DES synthesizing for a specific pollutant, as well as the low price prove their expected high potential for enhancing the removal of low water-soluble volatile organic compounds (VOCs) from the air in the biofiltration process. The aim of the project is to select two compounds of the DES type (one soluble, the other insoluble in the water phase) and to determine their influence on the course of removal of hexane and cyclohexane from the air in the biotrickling filtration process compared to the process carried out without modification of the liquid phase. The planned research results will answer the basic question about the possibility of using DES compounds and the mechanism of their action in biofiltration processes in order to improve the efficiency of air purification from hydrophobic VOCs. The successful implementation of the project will form the basis for the preparation of a project application in the field of applied research.