Olive stones, which are an abundant residue from the olive oil industry, were thermally and chemically treated to obtain a series of cheap activated carbons with fitted surface chemistry and porosity. These biomaterials were used as specific filters for gaseous emission treatments. Ethanol and n-octane were chosen as target VOCs. The performance of these filters in competitive VOCs adsorption processes and the influence of humidity were studied by analysing the corresponding breakthrough curves. Relationships between VOCs chemical nature, adsorbent characteristics and experimental conditions were discussed. Carboxylic acid groups play a specific role on the adsorption of polar molecules, because they determine the interaction strength. The adsorption rate for n-octane was significantly reduced when water or ethanol were present, while adsorption capacity was almost equivalent. The influence of humidity is stronger on ethanol adsorption process, specifically when more oxidized samples were tested. A new filter was developed by mixing hydrophobic and hydrophilic adsorbents in order to improve the simultaneous adsorption of ethanol and n-octane. In this case, the constant rate for competitive adsorption processes was favoured for both VOCs, regarding columns with a single adsorbent, because they were adsorbed on independent sites.