The present study aimed at maximizing the performance of a standard biotrickling filter (BTF) devoted to the treatment of CH4 at low concentrations by enhancing the mass transfer using optimum liquid recycling rates and an innovative gas recycling strategy. Internal gas recycling favored CH4 abatement in the early stages of BTF operation and supported stable elimination capacities (ECs) above 30 g m(-3) h(-1) at an empty bed residence time of 4 min and a liquid recycling velocity of 5 m h(-1) higher than most ECs achieved in single phase BTFs to date. The BTF exhibited a high microbial diversity (Shannon-Wiener indices of 2.5-2.8) dominated by Type I methanotrophs, likely due to the presence of high Cu2+ concentrations. Mass transfer limitations from the aqueous phase to the microorganisms, attributed to biomass accumulation in the packing material, were identified under the long term operation. (C) 2014 Elsevier B.V. All rights reserved.