The pretreatment of heavy oil refinery wastewater (HORW) was experimentally investigated using a three-dimensional electrode reactor (TDER) with granular activated carbon (GAC) and porous ceramsite particle (PCP) as the combination particle electrode and DSA (R) type anodes as the anode The results showed that higher chemical oxygen demand (COD) removal was obtained in TDER comparing with the two-dimensional electrode reactor (without particle electrodes packed) and combination particle electrode was favorable to improve the COD removal efficiency and reduce the energy consumption The treated HORW under the optimal experimental condition (GAC percentage = 75% current density = 30 mA/cm(2) pH not adjusted and treatment time = 100 min) presented that the removal efficiencies of COD total organic carbon and toxicity units were 45 5% 43 3% and 67 2% respectively and the ratio of 5-day biochemical oxygen demand to COD was increased from 010 to 029 which is beneficial for further biological treatment Furthermore the application of electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry to characterize polar compounds in HORW and their oxidation products was well demonstrated to reveal the composition variation (C) 2010 Elsevier Ltd All rights reserved