BACKGROUND: Acetone and methyl ethyl ketone (MEK) are commonly mixed together in the effluent streams from the manufacturing of semiconductors and optics-electronics. The metabolic activity on the biodegradation of two or more pollutants may involve induction, inhibition or co-metabolism, depending on the substrates and microbial species present. The compound interaction on the biochemical kinetic behaviours of an acetone and MEK mixture in a composite bead biofilter was investigated. RESULTS: The microbial growth rate and biochemical reaction rate of the two biodegraded compounds was inhibited and the inhibitive effect resulting from increasing the compound inlet concentration predominated at a higher compound inlet concentration for the single compound system. The microbial metabolic activity of biodegraded acetone in the microbial growth process and biochemical reaction process was inhibited as MEK was introduced and the inhibitive effect resulting from interaction of the compounds was more pronounced at higher MEK inlet concentrations and lower acetone inlet concentrations for the two compounds mixing system. The maximum elimination capacity of acetone and MEK for the two compounds mixing system was smaller and greater than those for the single compound system, respectively. CONCLUSION: The biodegradation rate of acetone in a biofilter would be inhibited as MEK was introduced. (C) 2010 Society of Chemical Industry