The present study investigated the influence of packing material characteristics on the electricity generation performance, treatment efficiency and degradation mechanism of petroleum pollutants over microbial fuel cells (MFCs) using petroleum refinery wastewater (PRW) as fuel. The granule graphite (GG) and granule-activated carbon (GAC) were used to MFCs as packing materials, respectively. GG-packed MFC showed the highest electricity generation and PRW treatment performance, power density (330.4 mWcm(-3)) and oil removal (84 +/- 3%) were both better than GAC-packed and non-packed MFCs due to the excellent electrical conductivity. GAC-packed MFC showed the most stable voltage output (higher than 200 mV for 576 h) and lowest mass transfer resistance than GG-packed and non-packed MFCs owing to the stronger adsorption ability. The properties of the packing materials affected the degradation mechanism of petroleum pollutants. Chain hydrocarbons were preferentially degraded in non-packed MFC; volatile phenols and benzene were preferentially removed in GAC-packed MFC; and all petroleum pollutants were simultaneously decomposed in GG-packed MFC. (C) 2015 Elsevier Ltd. All rights reserved.