Improved O3/H2O2 oxidation process for wastewater reclamation

A continuous two step O₃/H₂O₂ oxidation system, in which the waste gas from the former reactor was reused in the latter step with an ejector, was established for the purpose of wastewater reclamation in electronics industries. ORP monitor was combined into the system to obtain the optimum ratio of H₂O₂ to O₃ by automatically adjusting the dosage of H₂O₂, and ion exchange resin was used for removing organic acids formed during oxidation. The effectiveness of the O₃/H₂O₂ oxidation system for TOC removal was investigated under various conditions by using IPA, DMSO, and NMP as model substances. The optimum H₂O₂/O₃ for oxidizing IPA was in a range above 0.15, and it increased with the increase of O₃ dose. A sudden drop of ORP from ca. 800 mV to a little more than 200 mV was observed when H₂O₂/O₃ was approaching the optimum point from the lower end. An ORP between 250 mV and 300mV or 800 mV and 900 mV was proper for H₂O₂/O₃ control. The treatability of the model substances was in an order of IPA<<DMSO<NMP, being consistent with the magnitude of the energy of the highest occupied molecular orbital (eHOMO). The two step treatment system developed in this study was found to be more efficient than the conventional single step system. With the help of H₂O₂ dosing control and two step treatment using waste O₃, the system could save about 40% O₃ in comparison with the conventional O₃/H₂O₂ oxidation process.