Catalytic Ozonation Of Trace NDMA In Aqueous Solution On K-Co-Al₂O₃

Refractory organic pollutants in drinking water have become an important threat to people’s healthy. Since the removal efficiency of these pollutants by conventional water treatment process is poor, it is urgently needed to develop new advanced water treatment technology to remove refractory organic pollutants in water effectively.In this research, a series of K-Co-Al₂O₃ catalysts have been prepared and then coated on a honeycomb cordierite and their activities for catalytic ozonation of N-nitrosodimethylamine （NDMA） have been studied.The result shows when Al₂O₃ was calcined at 600℃, the removal efficiency of NDMA reaches 49%. The effect of some experiment parameters including catalyst dosage, initial pH of the solution, applied ozone dosage and initial concentration of NDMA on NDMA removal efficiency has also been studied.When loading transitional metal oxide on Al₂O₃ their catalytic activities were found to be improved. When the calcination temperature goes to 600℃, the catalysts loaded with transitional metal oxide follows the order of Co/ Al₂O₃﹥Ni/ Al₂O₃﹥Mn/ Al₂O₃﹥Cu/ Al₂O₃﹥Ce/ Al₂O₃, among them, Co/Al₂O₃ shows the highest activity. The activity of Co/Al₂O₃ increased significantly after adding additive metal potassium （K）. The removal efficiency of NDMA goes to 77% when the loading amount of Co is 2.5%, the loading amount of K is 1% and calcined at 600℃. Studies show that the optimal dosage of Co/Al₂O₃ is 167 mgL^-1, the optimal applied ozone dosage is 3 mgL^-1 and the optimal pH is 7.Monolithic honeycomb catalyst （K-Co-Al₂O₃-ceramic honeycomb） was prepared and showed high activity, NDMA removal efficiency went to 70% when monolithic honeycomb was used as catalyst. The water circulating flow rate and pore densities of ceramic honeycombs have negligible effect toward the NDMA removal efficiency. During the catalytic ozonation process little metal Co was found to leach out.Studies on the mechanism of the catalytic ozonation process showed that the presence of K-Co-Al₂O₃ and monolithic honeycomb catalyst significantly increased the absorption and decomposition of ozone in water. The activity of these two catalyst s is much higher than single Al₂O₃ and honeycomb. The presence of radical scavenger （t-butanol） restrain the ozonation process catalyzed by both K-Co-Al₂O₃ and monolithic honeycomb catalyst. These result shows that the catalytic ozonation process follow the Hydroxyl radical mechanism, the generation of H₂O₂ in catalytic ozonation process also support this mechanism. The structure and composition of K-Co-Al₂O₃ are characterized by BET, XRD and SEM. The results show that Co₃O₄ is the main active species in K-Co-Al₂O₃ catalyst. Ozone in water was adsorbed and decomposed on catalyst surface, and then the hydroxyl radicals were generated and diffused to solution to oxide NDMA.