Solutions of the synthetic dye Acid Red 211 (AR211), commonly used in many industries, were comparatively degraded using different supporting electrolytes under current-controlled electrolysis conditions. The efficiency of the electro-oxidation (EOx) approach with boron doped diamond electrodes (EOx/BDD) was examined by applying 100, 200, 300 and 400 mA with HCIO4, H2SO4 or Na2SO4 as a supporting electrolyte. Under similar experimental conditions, a diamond electro-Fenton (EF/BDD) system was used for treating synthetic dye solutions and was compared with the removal efficiencies obtained by EOx/ BDD. The results clearly showed that when AR211 was oxidized by employing the EF/BDD process with generation of free (OH)-O-center dot from the electrogeneration production of hydrogen peroxide (H2O2) and addition of Fe2+, the oxidizing power increased to 97% under the best conditions, with higher current efficiencies and lower energy consumption than those obtained by EOx/BDD. In this study, we also attempt to discuss critical evidence regarding the viability of the use of different supporting electrolytes because the results obtained in this research clearly demonstrated that the effect of the electrogenerated strong oxidant species depends on parallel mechanisms followed on the BDD surface, as well as the particular production of strong oxidants, such as the case of BDD((OH)-O-center dot) or BDD(SO4-center dot). (C) 2014 Elsevier B.V. All rights reserved.