This study investigated the feasibility of using lignin waste from pulp and paper industry as a mediator for treating ethanol stillage wastewater in microbial fuel cells (MFCs). Two configurations of MFCs used a salt-bridge and proton exchange membrane (PEM), and the influence of lignin and KMnO4 as mediators in PEM MFCs was evaluated. For salt-bridge MFC, graphite plates were used as cathode and anode while carbon cloth and graphite rods were substituted for cathode and anode in PEM MFC. The external resistance for both configurations was 550 +/- 50 Omega. Results showed that PEM MFC generated higher electric power with satisfactory treatment of wastewater. When lignin was added as a mediator in PEM MFC, the maximum power density increased to 93 W/m(2) with COD removal efficiency of about 81% after 6-day operation. This study showed the potential for the treatment of lignin-rich wastewater and ethanol stillage wastewater simultaneously with possibility of electric power generation. (C) 2014 Elsevier Ltd. All rights reserved.