Catalytic Ozonation Of Wastewater By Ac-tivated Alumina Or Cerium Supported Acti-vated Alumina

Advanced treatment of wastewater is the current research hotspot in the water pollution control field.Catalytic ozonation technology,which has been considered as one of the most promising advanced wastewater treatment technology,can effectively decompose bio-refractory organic pollutants and show its merits of high efficiency,easy-operation and no production of sludge.The key of the catalytic ozonation is to develop a catalyst with high ac-tivity and high stability.Herein activated alumina and cerium supported activated alumina were used in the catalytic ozonation of phenol solution and centralized industrial wastewater,and then evaluated in pilot scale.Phenol was selected as a model pollutant for the catalytic ozonation process.The results show that ozonation catalyzed by activated alumina can significantly improve the COD re-moval efficiency,and the calcination of the activated alumina can improve the catalytic activ-ity.The catalytic performance is optimized by calcination at 450?for 2 h.The characteriza-tion illustrates that the weak sites on activated alumina are the active centers for catalytic ozonation of phenol.After calcination the mineral of boehmite exsiting with activated alumi-na is converted to?-Al₂O₃,increasing the content of active component in the catalyst and the proportion of the weak acid sites,resulting in the improvement of the catalytic activity.The COD removal efficiency reaches 62%after 40 min treatment under the conditions of the cat-alyst dosage of 154 g/lL,ozone dosage of 70.5 mg/h and the neutral pH of the solution.The experiments indicate that the catalyst deactivation occurs alter 4 days reaction owing to the adsorption of the small molecular acid produced by phenol degradation on the active sites of the catalyst.Several metal oxides were coated on activated alumina to screen the active component.The sequence of the catalytic activity is as following:Ce/Al₂O₃>Ru/Al₂O₃>Mn/Al₂O₃?Cu/Al₂O₃?Fe/Al₂O₃>Al₂O₃.The best catalytic performance of Ce/Al₂O₃ is obtained with 1%?wt?Ce loading at 500?calcination for 1 h.The cerium coated on activated alumina presents in trivalent and tetravalent in the form of cerium oxides.The specific surface area,pore volume and pore size of Ce/Al₂O₃ decrease slightly as compared with activated alumina,however the phenol removal efficiency approaches 98.3%after 40 min treatment with cata-lyst dosage of 250 g/L and ozone dosage of 64 mg/h.The tert-butyl alcohol test demonstrates that oxidation degradation of phenol follows the·OH mechanism.Besides,the atomic oxygen as well as free radicals such as·OH2 is deemed to be the strong oxidizing agents in catalytic ozonation process.The catalyst performance shows little decrease after 15 days wastewater treatment,keeping the removal efficiency of phenol at 50-55%,which illustrates that the catalyst has good stability and high catalytic efficiency.The effluent from an aeration pool of a centralized wastewater plant was selected as tar-get pollutant to analyze the catalytic performance of the activated alumina and cerium sup-ported activated alumina.And then the activated alumina catalytic degradation of biochemical effluent in pilot scale was studied.The catalytic ozonation exhibits a good performance with 10-20 mg/L of COD removal and a remarkable decrease of the color from 32 to lower than 5 at effluent pH of 6-9.This study in semi-bench scale or pilot scale has demonstrated that the activated alumina and cerium supported activated alumina can both effectively catalytic ozonation degradation of organic pollutants.It should be pointed that the catalytic performance of the catalyst need to be further improved to meet the engineering project.