The effect of liquid distribution on the biological removal of propylene glycol methyl ether (PGME) in a trickle bed filter was investigated using a 0.3 m diameter column filled with 2-cm plastic spheres. Various liquid flowrates, bed heights (the ratio of bed height to bed diameter H/D = 2.3 and 4.6) and initial concentrations of PGME were used in experiments. The effect of initial liquid distribution was also examined using the multipoint (MPD) and single-point liquid distributors (SPD). The effect of liquid flow rate on liquid distribution, and hence, the BOD5 removal was found more significant for the short bed (H/D = 2.3). The BOD5 removal using MPD increased about 29% when the liquid flow rate was increased from 0.184 to 0.918 kg m(-2) s(-1). On the other hand, for H/D = 4.6 with both MPD and SPD, the effect of liquid flowrate on the BOD5 removal was insignificant although the dynamic liquid hold-up increased about two fold. It was also found that local distribution of the BOD5 removal corresponded well with local liquid distribution in the bed. In addition, a 37% decrease in the percentage BOD5 removal was observed while the BOD5 removal amount increased from 62 to 211 mg L-1 with increases in the initial concentration from 100 to 500 ppm. Based on the Monod kinetic model, the maximum BOD5 removal rate in the trickle bed filter was found to be 11.7 mg L-1 h(-1) and the Monod constant was 759 mg L-1. (C) 2007 Elsevier B.V. All rights reserved.