Behavior of hydrogen peroxide in electrolyzed anode water

Oxygen electrodes and spectrophotometric analysis have been used to evaluate the contribution of H2O2, in addition to available chlorine, to the high redox potential of electrolyzed anode water (EAW) with potassium chloride as an electrolyte. H2O2 was added externally to EAW, and the reaction between H2O2 and the available chlorine in the water was examined. EAW has a low pH (2.5), a high concentration of dissolved oxygen, and extremely high redox potentials (19 mg/l and 1,319 mV) when the available chlorine is at the concentration of about 580 microM. The addition of H2O2 to EAW led to H2O2 decomposition, and the amount of oxygen produced was equivalent to the amount of available chlorine. Oxygen production was reduced by ascorbic acid, and completely inhibited by 600 microM ascorbate. The rate of oxygen production was much affected by pH, and was slowest at or near pH 5.0. Rates were particularly high in alkaline solution. Absorbance at 235 nm (pH 3.0 and 5.0) and 292 nm (pH 10.0) decreased when H2O2 was added to the EAW at these pHs, and the extent of decrease was similar pH dependency to that of the oxygen production rate. Oxygen was not produced after H2O2 was added to EAW at pH 2.6 when available chlorine was absent, but oxygen was produced after potassium hypochlorite was added to such EAW. The oxygen production rates in EAW without available chlorine at pH 5.0 and 2.0, pH adjustment with KOH and HCl, respectively, were faster than the rate at pH 2.6, and fastest at pH 2.0. These results suggest that H2O2 or hydroxyl radicals derived from Fenton's reaction did not contribute to the high redox potential of EAW prepared with chlorine compounds as an electrolyte, so that the decomposition of H2O2 occurred rapidly with the reactions of chlorine and hypochlorite ions in EAW.