Advanced H₂O₂ oxidation for diethyl phthalate degradation in treated effluents: effect of nitrate on oxidation and a pilot-scale AOP operation

One of the objectives of this study was to delineate the effect of nitrate on diethyl phthalate (DEP) oxidation by conducting a bench-scale ultraviolet (UV)/H₂O₂ and O₃/H₂O₂ operations as suggested in a previous study. We also aim to investigate DEP oxidation at various UV doses and H₂O₂ concentrations by performing a pilot-scale advanced oxidation processes (AOP) system, into which a portion of the effluent from a pilot-scale membrane bioreactor (MBR) plant was pumped. In the bench-scale AOP operation, the O₃ oxidation alone as well as the UV irradiation without H₂O₂ addition could be among the desirable alternatives for the efficient removal of DEP dissolved in aqueous solutions at a low DEP concentration range of 85±15 μg/L. The adverse effect in the UV/H₂O₂ process was significantly greater than that in the UV oxidation alone, and its oxidation was almost halved by the nitrate. However, the nitrate clearly enhanced the DEP oxidation in the O₃ oxidation and O₃/H₂O₂ process. Especially, the addition of nitrate almost doubled the DEP oxidation efficiency in the O₃/H₂O₂ process. The series of pilot-scale AOP operations confirmed that about 30–50% of DEP dissolved in the treated MBR effluent streams was, at least, oxidized by the O₃ oxidation alone as well as the UV irradiation without H₂O₂ addition. The UV photolysis of H₂O₂ was most effective for DEP degradation with an H₂O₂ concentration of 40 mg/L at a UV dose of 500 mJ/cm².