In recent years, the in situ electrochemical generation of the Fenton reagent, also known as the electro-Fenton (EF) approach, has been studied in order to achievement the fact that the reduction of dissolved oxygen to hydrogen peroxide (H2O2) can be carried out selectively in acidic medium. This work describes the results obtained in the low flow plant (V = 3 L) with a boron doped diamond (BDD) as a cathode operating at constant current density, room temperature and liquid flow rate of 12 L min-1, employed for on-site H2O2 production in acidic medium (pH 3) to promote EF treatment. These processes were evaluated by their abilities to degrade a commercial methyl orange (MO) azo dye. Small quantities of generated carboxylic acids like ascorbic, benzoic, citric, maleic and oxalic acid were detected by HPLC determinations. Based on the use of a BDD cathode, is possible the effectively production of H2O2 in the medium via oxygen reduction. The dye MO was quickly removed during the first minutes of the treatment, yielding closely 80% of decolorization efficiency under optimized conditions and 7.66 kWh m-3 energy consumption. HPLC analysis confirmed that the MO degradation became effective.