Comparison of the rates of phenol advanced oxidation in deionized and tap water within a dielectric barrier discharge reactor

Electric non-thermalizing discharges provide promising novel means to induce oxidation of organic pollutants in water. The decomposition of phenol in solutions prepared with deionized (milliQ) and tap water was studied and compared in a Dielectric Barrier Discharge (DBD) reactor. Interestingly, a significant rate increase was found in tap with respect to milliQ water. Control experiments proved that this was not the effect of conductivity or of traces of iron or of residual active chlorine from the depuration process operated in the aqueducts of Italian cities. The same increase in efficiency as observed in tap water was instead obtained when phenol was treated in solutions containing bicarbonate anions in the same concentration as present in tap water, an effect attributed to buffering of the solution pH. The role of pH has been investigated thoroughly by measuring the process efficiency over a wide pH range, from 2 to 10, by using different buffer systems to probe reactivity at near neutral pH, the most relevant for drinking water applications, and by testing the effect of different buffer concentrations. These latter experiments failed to detect any significant kinetic effect attributable to the well known reactivity of bicarbonate as quencher of OH radicals.