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4. Conclusions In this study, the polyurethane sponge/TiO 2 composite carrier was used as a catalyst to catalyze the oxidation of papermaking wastewater. The highest COD reduction of 52% was observed at pH 9, an ozone concentration of 16 mg/L, a catalyst filling ratio rate of 7.5%, and a reaction time of 8 min, meanwhile, the color decreased from 3481 to 153 and the B/C value increased from 0.26 to 0.37. Compared with the ozonation system, the catalytic ozonation system had a better effect on COD reduction, chroma, B/C value and SS. Kinetic studies showed that both ozonation and catalytic ozonation conformed to pseudo-first- order kinetics. The reaction rate constant of catalytic ozonation was significantly higher than that of ozonation. The GC-MS results showed that the catalytic ozonation system was effective in degrading DCS, as stilbene and palmitic acid were completely degraded; it could be concluded that it is suitable for treating water that can be reused in different papermaking processes. Furthermore, the degradation path and mechanism of stilbene and palmitic acid were deduced. In sum, this study improves our understanding of catalytic ozonation mechanism of DCS and provides technical references for closed water cycle paper mills. All nine esters in the raw water were removed, and many small molecules were generated, which indicated that the large molecules were effectively decomposed. There is also a good treatment effect for organic substances such as palmitic acid and styrene that affect wastewater reuse. That is, palmitic acid and styrene were decomposed entirely at the end of the reaction. This proved that ozone catalysis could treat pulp and paper mill wastewater efficiently and provide a new idea for wastewater treatment technology. Author Contributions: C.Z.: Writing—original draft, Conceptualization, Methodology, Software, Formal analysis, Writing—review & editing; J.Z.: Data curation, Investigation, Visualization; Y.C.: Validation, Visualization; J.X.: Funding acquisition, Project administration, Supervision. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by the National Natural Science Foundation of China, grant number [No. 21968005]. And Guangxi BaGui Scholars Program, grant number [2019A33]. Data Availability Statement: Not applicable. Acknowledgments: The authors gratefully acknowledge financial support for this work from the
National Natural Science Foundation of China (No. 21968005). Conflicts of Interest: The authors declare no conflict of interest.
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