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Highlights • The effect of O 2 -ionized products on HgO oxidation is greater than that of H 2 O-ionized products in WESP. • H 2 O played an inhibitive effect on Hg0 removal in WESP. • Wash-down by the water film had slight effect on Hg0 removal rate. Abstract The elemental mercury (Hg0) removal performance of wet electrostatic precipitator (WESP) was studied on a lab-scale experimental device. Increasing voltage in WESP promoted the Hg0 oxidation because higher-energy electrons in the electric field accelerated the discharge of O 2 and H 2 O to form free radicals like O, O 3 and OH. The oxidation of Hg0 by O 2 -ionized products was the dominant pathway for Hg0 removal in WESP. H 2 O played an inhibitive role in Hg0 removal. The presence of H 2 O competed with O 2 for electron energy to form OH, thus inhibiting the generation of O and/or O 3. The OH could oxidize Hg0 into HgOH; however, HgOH tended to decompose and release as Hg0. The wash-down effect of water film could collect part of Hg0, which could partly offset the inhibitive effect of H 2 O on Hg0 removal. As Hg0 is insoluble, the Hg0 removal by wash-down of the water film was insignificant in WESP. Mercury re-emission existed in WESP because of the water-insolubility of Hg0 and the instability of HgOH. The findings indicate that oxidizing Hg0 by radicals in the electric field of WESP might be a feasible method for removing Hg0 from power plants. [ABSTRACT FROM AUTHOR]