Rhodococcus sp. BTO62 was isolated from activated sludge from a wastewater treatment plant as an o-xylene-degrading microorganism. BOT62 degraded not only o-xylene, but also benzene, toluene, ethylbenzene, m- and p-xylenes and styrene (BTEXS). A laboratory scale biofilter packed with Biosol as packing material, which is made from foamed waste glass mixed with corrugated cardboard, was inoculated with strain BTO62 and operated to remove relatively high loading of o-xylene at different space velocities under non-sterile and sterile conditions. The o-xylene elimination capacity to maintain more than 90% removal efficiency was 41 g/m(3)/h under sterile condition, but it enhanced to 160 g/m(3)/h under non-sterile condition. This indicates possibilities of the role of other contaminants for degradation of o-xylene and the degradation of intermediate products of o-xylene by contaminants. Quick recovery of o-xylene degradation was observed after shutdown of o-xylene gas supply and mineral medium circulation for 10-30 days. (C) 2007 Elsevier B.V. All rights reserved.