Electrochemical pretreatment (EP) with a pair of Ti/RuO2 mesh plate electrodes was applied to solubilize waste activated sludge (WAS) with the aid of hypochlorite, and the conventional pretreatment methods of thermal pretreatment (THP), thermal-alkaline pretreatment (TAP) and alkaline pretreatment (AP) were also introduced as the comparative cases. In this study, Growth Rate of Solubilization (GRS) was developed to characterize the solubilization process of WAS in terms of SCOD (soluble chemical oxygen demand), carbohydrates, proteins, VFAs, and the highest GRS (SCOD) was found in EP-group, with approximately 5.2 times higher than that in AP group. Around 647 L/kgVS (volatile solids) of biogas was obtained in EP-group, which was up to 63.4% more than that in the control group (396 L/kgVS), and the corresponding VS removal efficiency reached to 45.5%. Therefore, EP might be a promising enhancement method for sludge solubilization, and thus contribute to the anaerobic digestion process. (C) 2014 Elsevier Ltd. All rights reserved.