The surface passivation and the subsequent reduction of ZVI reactivity seriously restricted the application of zero-valent-iron (ZVI) for water remediation. This study comprehensively investigated the critical role of common oxidants, such as O-2, H2O2, KMnO4 and CrO42- in activating the reactivity of ZVI surface and hence in facilitating nitrate reduction from the aqueous solution at non-acidic pH. Nitrate reduction by ZVI was negligible in the absence of O-2 at pH > 5. To the contrary, obvious reduction of nitrate was observed in the presence of O-2, although with a clear trend of decreasing nitrate reduction with pH increase. KMnO4, H2O2, and CrO42- were observed to strongly enhance the reactivity of ZVI. Dosing KMnO4 and H2O2 achieved 94% and 97% of nitrate reduction at pH 5.0, and 74% and 98% at pH 7.0. Five cycles of nitrate removal by the combined system of ZVI/oxidant/zeolite demonstrated the overcoming of the impedance of passivation layer, strongly facilitating the ultimate removal of nitrogen species from the aqueous solution. (C) 2015 Elsevier B.V. All rights reserved.