A facilitated transfer membrane-aerated biofilm reactor (FT-MABR) was designed to overcome feed flow short-circuiting and achieve facilitated mass transfer. In the FT-MABR, the flow velocity was uniform and the flow direction was almost perpendicular with the hollow fiber membranes. The effects of feed flow velocity on COD, ammonium and total nitrogen (TN) removals were investigated through a long-term process study. With the increase of flow velocity, resistance impact load capability and oxygen utilization efficiency of the FT-MABR were enhanced. Meanwhile, ammonium was removed preferentially compared with COD. Batch studies indicated that, at the feed flow velocity of 0.05 m/s, when COD/N ratios were 3, 5 and 7, the TN removal efficiency reached to 50.7%, 72.8% and 83.5%, respectively. The process study further illustrated that the increase of feed flow velocity significantly strengthened the accumulation of nitrite and TN removal in the FT-MABR. The FT-MABR is a feasible technology for the treatment of wastewater with low COD/TN ratio. The further research will focus on the effect of feed flow velocity on the biofilm structure and build a mathematical model based on microbial kinetics and hydrodynamics. (C) 2011 Elsevier B.V. All rights reserved.