The influence of applied voltage on the bioelectrochemical anaerobic digestion of sewage sludge was studied at ambient temperature (25 +/- 2 degrees C). The stability of the bioelectrochemical anaerobic digestion was considerably good in terms of pH, alkalinity and VFAs at 0.3 V and 0.5 V, but VFA accumulation occurred at 0.7 V. The specific methane production rate (370 mL CH4/L.d) was the highest at 0.3 V, but the methane content (80.6%) in biogas and the methane yield (350 mL CH4/g CODr) were higher at 0.5 V, significantly better than those of 0.7 V. The VS removal efficiency was 64-66% at 0.3 V and 0.5 V, but only 31% at 0.7 V. The dominant species of planktonic microbial communities was Cloacamonas at 0.3 V and 0.5 V, but the percentage of hydrolytic bacteria species such as Saprospiraceae, Fimbriimonas, and Ottowia pentelensis was much higher at 0.7 V. The optimal applied voltage for bioelectrochemical anaerobic digestion was 0.3-0.5 V according to digestion performance and planktonic microbial communities. (C) 2016 Elsevier Ltd. All rights reserved.