Electrochemical disinfection in chloride-free electrolyte has attracted more and more attention due to advantages of no production of disinfection byproducts (DBPs), and boron-doped diamond (BDD) anode with several unique properties has shown great potential in this field. In this study, inactivation of Escherichia coil (E. coli) was investigated in Na2SO4 electrolyte using BDD anode. Firstly, disinfection tests were carried on at different current density. The inactivation rate of E. coli and also the concentration of hydroxyl radical ((OH)-O-center dot) increased with the current density, which indicated the major role of (OH)-O-center dot in the disinfection process. At 20 mA cm(-2) the energy consumption was the lowest to reach an equal inactivation. Moreover, it was found that inactivation rate of E. coil rose with the increasing Na2SO4 concentration and they were inactivated more faster in Na2SO4 than in NaH2PO4 or NaNO3 electrolyte even in the presence of (OH)-O-center dot scavenger, which could be attributed to the oxidants produced in the electrolysis of SO42-, such as peroxodisulfate (S2O82-). And the role of S2O82- was proved in the disinfection experiments. These results demonstrated that, besides hydroxyl radical and its consecutive products, oxidants produced in SO42- electrolysis at BDD anode played a role in electrochemical disinfection in Na2SO4 electrolyte. (C) 2010 Elsevier Ltd. All rights reserved.