Fuel recovery from sewage sludge is a promising energy production method, which can simultaneously address energy issue and environmental concerns associated with waste treatment. This study evaluates power productions from different types of sewage sludge in microbial fuel cells (MFCs) with energetic and microbiological perspectives. Results show that the recovered organic matter (ROM), a kind of anaerobic sewage sludge, is a good candidate for bioelectricity generation compared to conventional waste activated sludge (WAS), giving a maximum power output of 38.1 W m(-3). The lower internal resistance of the MFC fed with ROM is attributed to the higher concentration of soluble chemical oxygen demand (SCUD) in the anolyte. At a nominal solid retention time of 8 day, 60.2 +/- 4.9% of the total COD in the ROM is removed. The initial chemical composition and microbial consortium in ROM demonstrates the highest exoelectrogenesis potential compared with other WAS samples. The syntrophic communities formed on the surface of anode electrodes enable the successful conversion of the substrates into bioelectricity. Although the recovered energy cannot outweigh the operation costs of the bioelectrochemical systems, the total expenditure for ROM treatment herein is reduced by 30-50% compared to those for WAS. (C) 2013 Elsevier B.V. All rights reserved.