The paper outlines treatment of waste gas containing monochlorobenzene (MCB) and benzene in a mixture using biofilter packed with compost and woodchips seeded with Acinetobacter calcoaceticus. The biofilter could treat waste gas containing MCB and benzene effectively with an efficiency of (99 +/- 5%) and (97 +/- 6%) at optimal empty bed contact time (EBCT) of 3 min with a loading of 57 g/m(3)/h of MCB and 2 g/m(3)/h of benzene. At optimum loading of MCB and benzene, the biofilter showed total bacterial count of 13 x 10(5) CFU/g of compost, while the MCB and benzene degrading bacterial count was 71 x 10(4) CFU/g and 5 x 10(4) CFU/g compost respectively. The experimental removal efficiency of MCB and benzene were in good agreement with the model predicted value. (C) 2010 Elsevier Ltd. All rights reserved.