Advanced Treatemnt Of Coal Chemical Wastewater By Catalyzed Ozonation With Metal-supported Alumina

The coal chemical wastewater has a large discharge volume,high chroma,and complex water quality components.Its tail water still contains a large amount of refractory organic pollutants after bio-treated.Heterogeneous catalytic ozonation technology is an efficient,economic,safe,and green advanced treatment technology.It has shown good application prospects in the field of advanced treatment of industrial wastewater.The performance of the heterogeneous catalyst is crucial to determine the application efficiency of this technology.The oxides of Mn,Ti and Mg are commonly used heterogeneous catalysts.In view of the various kinds of organics in coal chemical wastewater,a single type of catalyst often cannot achieve satisfactory catalytic performance.Therefore,the development of metal composite catalysts which are suitable for coal chemical wastewater has greater practical significance.Thus,this study chose to support Mn,Ti and Mg elements on the activeγ-Al₂O₃ pellets to prepare a metal-supported catalyst and use it in the catalytic ozonation of coal chemical wastewater.The effects of metal loading,calcination temperature and other preparation conditions on the catalyst activity were investigated and the catalytic activity of single-component,two-component,and three-component metal-supported catalysts was compared.The results showed that the catalytic performance of Mn/Al₂O₃ was significantly better than that of Ti/Al₂O₃ and Mg/Al₂O₃ among the single-component catalysts.The catalytic activity of the two-component catalysts was lower than that of Mn/Al₂O₃,while the three-component catalysts showed a synergistic effect to a certain extent.The Mn-Ti-Mg/Al₂O₃ catalyst exhibited the best catalytic performance which was prepared under the conditions of calcination temperature of 550°C and Mn,Ti,and Mg element loadings of 1.5%,3.0%,and 2.0%.It can make the removal rate of COD and UV₂₅₄ in wastewater reached 69.27%and 91.22%respectively.Several metal-supported catalysts have unobvious adsorption capacity for organic pollutants in coal chemical wastewater,indicating that the degradation of organics mainly depends on the catalytic ozonation process.In addition,the metal-supported catalysts have a strong decomposing effect on liquid ozone molecules and its catalytic activity is positively correlated with its ability to decompose ozone.Several single-component,two-component and three-component metal-supported catalysts with better catalytic performance were characterized by SEM,EDS,BET,XRD,XPS,pH_pzc and other properties.The results showed that the average pore diameter of the Al₂O₃ carrier increases wheras the specific surface area decreases after the metal was supported.And there is a good correlation between the specific surface area and the catalytic activity of the metal-supported catalysts.Mn,Ti and Mg elements of the catalysts mainly exist in the form of MnO₂,TiO₂,and Mg O.Besides,the isoelectric point of catalysts has been decreased with the metal was loaded.The effect of experimental conditions on the catalytic performance of Mn-Ti-Mg/Al₂O₃ was investigated in catalytic ozonation process.The results showed that the increase of catalyst dosage,ozone dosage,and solution pH can further improve the removal efficiency of COD in wastewater.After coal chemical wastewater was treated by Mn-Ti-Mg/Al₂O₃ catalyzed ozonation,the COD,BOD₅,NH₃-N and other indicators meet the pollutant emission standards for the coking chemical industry（GB16171-2012）.GC-MS analysis results showed that a total of 28organic pollutants were detected in coal chemical wastewater,which was mainly phenol pollution.The kinds and total peak area of organic substances detected in the wastewater have been greatly reduced after the wastewater was treated by catalyzed ozonation.