High current density of 10.0-14.6 A/m(2) and COD removal up to 96% were obtained in a microbial electrochemical cell (MEC) fed with digestate at hydraulic retention time (HRT) of 4 d and 8 d. Volatile fatty acids became undetectable in MEC effluent (HRT 8 d), except for trivial acetate (4.16 +/- 1.86 mg COD/L). Accumulated methane only accounted for 3.42% of Delta COD. Pyrosequencing analyses showed abundant fermenters (Kosmotoga spp.) and homoacetogens (Treponema spp.) in anolytes. In anode biofilm, propionate fermenters (Kosmotoga, and Syntrophobacter spp.), homoacetogens (Treponema spp.), and anode-respiring bacteria (ARB) (Geobacter spp. and Dysgonomonas spp.) were dominant. These results imply that syntrophic interactions among fermenters, homoacetogens and ARB would allow MECs to maintain high current density and coulombic efficiency. (C) 2013 Elsevier Ltd. All rights reserved.