Laboratory experiments were conducted to determine the potential for removing 1,2-dichlorobenzene (1,2-DCB) in gaseous phase by biofiltration. Experiments were carried out over 8 months in a steel tank (0.45 m(3)) using an organic filter medium composed of peat, maple wood chips, chicken manure and 1,2-DCB-contaminated soil. During the first 6 months, the biofilter was operated without injecting 1,2-DCB in order to characterize the physicochemical, mechanical and microbiological properties of the filter bed. The results revealed that it is an excellent medium for both microbial development (up to 10(9) cells g(dry soil)(-1) for heterotrophic bacteria) and long-term stability with a limited drop dry of pressure (30 cm of water) and no clogging. Over the final 2 months, the biofifter treated air laden with 1,2-DCB (0.30 and 0.75 g m(-3)) and the maximum elimination capacity reached was 9 g m(-3) h(-1) (inlet load of 13 g m(-3) h(-1)), which represented 69% efficiency. Elimination performance was strongly dependent upon inlet concentration, sorption/desorption and biodegradation phenomena occurring in the filter medium. Sorption/desorption and biodegradation mechanisms during the start-up period were characterized using the elimination efficiency (%). At the beginning of the 1,2-DCB injection, the microorganisms were strongly impacted and sorption/desorption phenomena prevailed. With the decrease of the inlet concentration, biodegradation progressively increased to become the most important mechanism. It was concluded that biofiltration possesses an excellent potential for treating volatile chlorinated benzene, known to be recalcitrant to biodegradation. (C) 2003 Society of Chemical Industry.