Hydrogen peroxide was produced by direct current electrolysis using only two electrodes, a carbon felt cathode and a RuO2 coated titanium anode. The required oxygen was supplied by oxidation of water and by transfer from the atmosphere or by pure oxygen injection. The current was maintained below a maximum value to avoid peroxide reduction. A high peroxide production rate was reached and a 15 mg l(-1) concentration was maintained. The electrolysis removed turbidity and dissolved organic carbonaceous compounds from municipal sewage plant effluents. Real effluents were significantly disinfected owing to the direct effect of electric current and the indirect effect of peroxide. A residual effect was also observed.