Catalytic ozonation for water and wastewater treatment: Recent advances and perspective

Ozonation process has been widely applied in water and wastewater treatment, such as for disinfection, for degradation of toxic organic pollutants. However, the utilization efficiency of ozone is low and the mineralization of organic pollutants by ozone oxidation is ineffective, and some toxic disinfection byproducts (DBPs) may be formed during ozonation process. Catalytic ozonation process can overcome these problems to some extent, which has received increasing attention in recent years. During catalytic ozonation, catalysts can promote O3 decomposition and generate active free radicals, which can enhance the degradation and mineralization of organic pollutants. In this paper, the history of ozonation application in water treatment was briefly reviewed. The properties of the ozone molecule, the ozonation types and several ozone-based water treatment processes were briefly introduced. Various catalysts for catalytic ozonation, including homogeneous and heterogeneous catalysts, such as metal ions, metal oxidizes, carbon-based materials and their possible catalytic mechanisms were analyzed and summarized in detail. Furthermore, some inconsistent results of previous research on catalytic ozonation were analyzed and discussed. The application of catalytic oxidation for the degradation of toxic organic pollutants, including phenols, pesticides, dyes, pharmaceuticals and others, was summarized. Finally, several key aspects of catalytic ozonation, such as pH effect, the catalyst performance, the catalytic mechanism were proposed, to which more attention should be paid in future study.