The average values of r2 for BTEX at all steady state operating days were found to be greater than 0.99 but at the day 83, the average value was only 0.9823. Qi et al. (2005) observed the same trend for methyl propyl ketone, MEK, toluene and n-butyl acetate mixture removal in biofilters inoculated with fungus Cladosporium sphaerospermum and packed with polyurethane, and concluded that n-butyl acetate was the most quickly degradable followed by MEK, methyl propyl ketone and then the toluene (Qi et al., 2005).