Catalytic removal of chemical oxygen demand during ozonation of the simulated wastewater from coal chemical industry

Simulated wastewater samples, representative of coal chemical industry and comprising major constituents such as phenol, p-cresol, o-cresol, and naphthalene, were subjected to treatment in a range of catalytic ozonation systems. To prepare the catalysts for ozonation, three series of metal oxides, iron oxides, manganese oxides, and cerium oxides, were manufactured onto the surface of γ-Al2O3 support in varying loadings. The determination of the optimal loading amount for each catalyst was based on the observed removal efficiency of chemical oxygen demand (COD) in phenol-containing aqueous solution. Primary small molecular organic acids formed in the aqueous solution during the degradation of phenol were analyzed by ion chromatography. The decomposition of ozone without catalyst can directly oxidize phenol, and catalytic ozonation can reach the same goal through the generation of OH. The synergy effects between ozone and the catalysts facilitate the production of highly reactive oxidizing species, leading to more efficacious degradation of phenol and an increased total concentration of organic acids till 37.8 mg/L. Radical capture experiments revealed that the generation of OH within the catalyzed ozonation system is associated with the presence of oxygen defects on the catalyst's surface, which significantly influenced the catalytic efficacy during the ozonation process. A loading of 20 %CeO2 on γ-Al2O3 support exhibited the best COD removal rate as high as 90 % due to the increased availability of lattice oxygen participating in catalytic ozonation. Thus, the methodology built for the optimization of ozonation catalyst is proven a promising way to prepare candidate catalyst for the treatment of wastewater from coal chemical industry.