This study investigated the effects of filter media types and nitrate (NO3-) concentrations in nutrient solutions on C2H4 biofiltration. A new nutrient solution with zero NO3- concentration was supplied to two perlite-bed biotrickling filters, two perlite-bed biofilters, and two GAC (Granular Activated Carbon)-bed biofilters, while the other with 2 g L-1 of NO3- was used for the other two GAC biofilters. All reactors underwent a total test duration of over 175 days with an EBRT (Empty Bed Residence Time) of 30 s, inlet gas flow rate of 7 L min(-1), and inlet C2H4 concentrations of 20-30 mg m(-3). NO3- concentration and media type significantly affected the C2H4 removal efficiencies in all types of biofiltration. The perlite media with no NO3- achieved C2H4 removal efficiencies 10-50% higher than the others. A NO3- concentration as high as 2 g L-1 in the original nutrient solution may act as an inhibitor that suppresses the growth or activity of C2H4 degraders. In addition, the perlite media resulted in higher C2H4 removal efficiencies than GAC media, because the hydrophilic surface of the perlite leads to a higher moisture content and thus to favorable microbial growth. (C) 2012 Elsevier B.V. All rights reserved.