The degradation of individual and mixed benzene and ethylene in activated carbon biofilters inoculated with a microbial consortium was investigated. The benzene biofilter was capable of achieving a benzene removal efficiency of 96% at a residence time of 2 min and an inlet concentration of 700 mg m(-3). During operation with an inlet benzene of 700 mg m(-3), the maximum elimination capacity of the biofilter was 483 g of benzene m(-3) day(-1). The ethylene biofilter was capable of achieving an ethylene removal efficiency of up to 100% at a residence time of 14 min and an inlet concentration of 331 mg m(-3). Under these conditions, the maximum elimination capacity of the biofilter was 34 g of ethylene m(-3) day(-1). For removal of mixed compounds (inlet benzene = 509 mg m(-3) and ethylene = 354 mg m(-3)), a residence time of 10 min was optimal. With this residence time, the maximum elimination capacity for benzene and ethylene was 74 g of benzene m(-3) day(-1) and 48 g of ethylene m(-3) day(-1), respectively. Biofilters inoculated with the microbial consortium (Bacillus or Pseudomonas strains) provide an attractive treatment technology for removing individual and mixed benzene and ethylene. (C) 2003 Elsevier Science Ltd. All rights reserved.