An air-cathode microbial fuel cell (MFC) is an efficient and sustainable MFC configuration for recovering electrical energy from organic substances. In this paper, we developed a graphite-granule anode, tubular air-cathode MFC (GTMFC) capable of continuous electricity generation from glucose-based substrates. This GTMFC produced a maximum volumetric power of 50.2 W m(-3) at current density of 216 A m(-3) (R-EX = 22 Omega). Electrochemistry impedance spectroscopy (EIS) measurements demonstrated an overall internal resistance of 27 Omega, consisting of ohmic resistance of R-ohm = 13.8 Omega(51.1%), a charge-transfer resistance of R-c = 6.1 Omega (22.6%) and a diffusion resistance of R-d = 7.2 Omega (26.3%). Power generation with respect to initial chemical oxygen demand (COD) concentration was described well by an exponential saturation model. Recirculation was to found to have a significant effect on electrochemical performance at low COD concentrations, while such effect was absent at high COD concentrations. This study suggests a feasible and simple method to reduce internal resistance and improve power generation of sustainable air-cathode MFCs. Crown Copyright (C) 2007 Published by Elsevier B.V. All rights reserved.