The control of liquid flow is one of the most significant factors that affect operation of biotrickling filters. This study evaluated removal of ethylene (C2H4) using biotrickling filters at various liquid recirculation flow rates. Perlite and glass beads were utilized as media in eight and two reactors, respectively. Trickle liquid recirculation flow rates ranging from 2.7 to 26 L h(-1) (velocity of 0.4-3.7 m h(-1)) were used. Two perlite reactors were operated with the liquid being recirculated intermittently for 10 min every hour at a recirculation flow velocity of 13 L h(-1) (velocity of 1.9 m h(-1)). Inlet gas contained about 30 mg m(-3) of C2H4 and 0-40 mg m(-3) of ammonia (NH3). The results showed that C2H4 removal efficiencies increased as time elapsed, but the increasing rate of C2H4 removal was different based on the reactor types. One of the two perlite biotrickling filters with low liquid recirculation flow exibited a high C2H4 removal up to 90%, but other biotrickling filters reached only about 40-70% of C2H4 removal efficiency, due to either a relatively high mass transfer limitation or poor distribution of nutrients. This study denotes that a trickle liquid flow over 0.8 m h(-1) (5.4 L h(-1)) had a significant detrimental effect on ethylene removal due to high mass transfer limitation that suppresses microbial growth for ethylene degradation. Therefore, the perlite biotrickling filters with flow rates as low as 0.4 m h(-1) (2.7 L h(-1)) can gave the best performance in high ethylene removal. (C) 2009 Elsevier B.V. All rights reserved.