The performance and microbial communities of two differently inoculated biotrickling filters (BTFs) treating chlorobenzene (CB) were compared. The previously isolated Ralstonia pickettii L2 was employed to enhance the performance of BTF. The two separate BTFs (BTF-1 and BTF-2) were initially inoculated with the previously isolated Ralstonia pickettii L2 + sludge and sludge, respectively. The bioaugmented BTF-1 showed a faster start-up, with over 90% CB removal from day 14 onwards, while BTF-2 without bioaugmentation reached 88% CB removal on day 35. BTF-1 also exhibited considerably better CB removal and mineralization capacity. The maximum elimination and mineralization extent of BTF-1 and BTF-2 were 117 g m(-3) h(-1) and 91.6%, and 89 g m(-3) h(-1) and 82.1%, respectively. Quantitative monitoring of the introduced bacterial strain was performed with a real-time PCR protocol. Real-time PCR and DGGE both gave consistent results regarding the presence of Ralstonia pickettii L2 during the whole operation of BTF-1. The inoculated strains were exclusively found in the BTF-1 in which it was added, and remained persistent throughout the whole operation, indicating a successful bioaugmentation. The bioaugmented BTF was shown to be a possible alternative technology for the treatment of waste gas containing CB or other recalcitrant compounds. (C) 2015 Published by Elsevier B.V.