Compounds interaction on the biodegradation of acetone and methyl ethyl ketone (MEK) mixture in a composite bead biofilter was investigated. The biodegradation rate of two compounds in the exponential growth phase and stationary phase for the single compound and two compounds mixing systems was determined. The microbial growth rate and biochemical reaction rate of biodegraded two compounds was inhibited at 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 by introducing MEK and was more pronounced at higher MEK inlet concentration and lower acetone inlet concentration for the two compounds mixing system. The maximum elimination capacity of acetone and MEK for the single compound system was smaller and greater than those for the two compounds mixing system, respectively. (C) 2009 Elsevier Ltd. All rights reserved,