BACKGROUND: Degrading hydrophobic volatile organic compounds in biofilters is very challenging. Previous research in our laboratories examined the degradation of hydrophobic contaminants by several methods including changing the empty bed resident time, utilization of surfactants and change of the microorganism consortium. As n-hexane is considered relatively soluble in benzene and alongside benzene is more soluble in water, it was anticipated that a mixture of both volatile organic compounds fed to a trickle bed air biofilters (TBABs) would lead to an improved performance of n-hexane degradation. RESULTS: The ratio of benzene:n-hexane studied was 2 : 1 by volume, corresponding to a concentration ratio of 3 : 1, respectively. The TBAB was operated at pH 4 to provide favorable conditions for fungi growth. The effects of changing loading rates ranging from 20 to 80 g m(-3) h(-1) on the biofilter performance, acclimation period, and removal profile along biofilter depth, nitrogen consumption and CO2 production were studied under continuous loading operation conditions and compared to previous data of TBABs degrading single feed of benzene and n-hexane separately. CONCLUSIONS: Results have shown that the degradation of n-hexane is significantly impacted by the presence of benzene; however, the degradation of benzene was not impacted to the same extent as n-hexane. (C) 2010 Society of Chemical Industry