This paper proposes the use of natural fibres: cotton, hemp and jute as an additive to the fills in peat-bark biofilters used to deodorise nuisance industrial gases in order to increase the sorption properties of the biomass used. The subject of the studies was waste gases from a grease trap, which were passed through biofilters to remove volatile fatty acids (VFAs) from them that are responsible for the odour nuisance of these gases. Gases were sampled upstream and downstream of the beds and analysed qualitatively and quantitatively on a gas chromatograph. Based on the changes in volatile fatty acid concentrations, the efficiency of the deodorisation process was evaluated. The deodorisation results were compared between the individual beds at the unstable stage of those beds filtration, i.e. during the period of biofilters activation and during their stable filtration. For each bed, the efficiency during each week of filtration was calculated. The efficiencies of removal of individual fatty acids from the waste gases were also compared. The studies show that a 3-month filtration period of the biofilter is sufficient for the biological bed to begin to effectively perform its function as a deodoriser of nuisance waste gases under industrial conditions. This period was characterised by considerable turbulence and activation of both the filter material and the microorganisms in the bed. During the first weeks of activation, the beds described in this paper showed relatively low deodorisation efficiencies (33-58 %). In the next phase, there was an increase in flow resistance and a partial decrease in treatment effects to 32 - 47 %. After that, there were fluctuations in deodorisation efficiency for several weeks until the microflora was established and adapted. During this period, the peat-bark bed had the best efficiency amounting to 70 - 80 %. After 9 weeks, the beds were already partially activated, the microorganisms were moving towards equilibrium and the deodorisation efficiency with fibre beds was above 80 %. After 15 weeks of filtration, the already activated biofilters reached efficiencies of over 90 % and even 95 % in the case of cotton.