The Study On Ozonation/Catalytic Ozonation For The Degradation Of Phenoxyacetic Acid And Phenazone

With the development of Chinese pharmaceutical industries, the wastewater emission has gradually become one of the most important pollutants, which is a kind of refractory and toxic wastewater with the shortcoming of complex component, wide fluctuation of concentration, strong toxicity and feeble biochemical degradation. Phenoxyacetic acid and phenazone were chosen as subjects of the study, the effect of different experiment parameters on their degradation by ozonation alone was studied and the degradation mechanism in ozonation process was explored. The reaction rate constants(kO3) were determined by absolute method or competitive kinetics method. Based on the homemade magnetic cerium dioxide, the catalytic performance and effect for the degradation of simulated pharmaceutical wastewater were investigated. The element composition and reaction mechanism during catalytic ozonation process were analyzed. The main results were as follows:1. Phenoxyacetic acid(PAA) was selected as the model pollutant. The degradation of PAA in aqueous solution has been investigated under a variety of conditions by ozonation. The effect of various parameters such as the pH value, the initial concentration of PAA and the ozone dosage were studied by the depletion in the concentration of PAA. The main intermediates produced in the ozonation process were detected by GC/MS and HPLC techniques and a possible degradation pathway of PAA was proposed. The kinetics analysis was deduced based on the reaction rate constant. The results showed that a high removal of PAA achieved at all conditions. Compared with acid conditions, the PAA removal of alkaline conditions(8.0, 10.0 and 12.0) was improved from 64% to 78% after 60 min. The PAA removal obviously decreased when the initial PAA concentration increased from 100 to 2000 mg·L-1. The PAA removal increased with the increase of ozone dosage. The PAA degradation followed pseudo-first-order kinetics. In view of diffusion and mass transfer, the reaction was proved to be in slow kinetic regime of the gas–liquid reaction and finally the kinetic constant ki was built.2. Phenazone(PZ) was selected as the model pollutant. The degradation of PZ in aqueous solution has been investigated under a variety of conditions by ozonation. The effect of various parameters such as the p H value, the initial concentration of PZ and the ozone dosage were studied by the depletion in the concentration of PZ. A series of intermediates formed in the ozonation process were detected by GC/MS and HPLC techniques and a possible degradation pathway of PZ was proposed. The effect of tert-butyl alcohol was discussed simultaneously and the kinetics analysis was revealed. The results showed that the pH value had no effect on the PZ removal ranged from 3.0 to 11.0, the PZ removal was proportional to the ozone dosage and was inversely proportional to the initial PZ concentration. The PZ degradation also followed pseudo-first-order kinetics and the corresponding model was proposed as an exponential function of 1.2735 0.91400 O3 0[PZ] [PZ] exp( 0.37 Q [PZ] t)-= -. At last,the kinetic constant kO3(8.12×105 M-1s-1) was determined by competitive kinetics method.3. The homemade magnetic cerium dioxide was applied to the catalytic ozonation of phenazone(PZ). The effect of the p H value, the initial concentration of PZ, the ozone dosage, the catalyst dosage and the cerium loading content was investigated. The reaction mechanism on catalytic ozonation was analyzed. The results showed that the PZ removal was improved after the addition of catalysts in water. The magnetic cerium dioxide was proved to have the best catalytic activity, the final PZ removal rate could reach 88%, 9% more than that in ozonation alone. It was considered to be attributed to surface reactions. At first, the organics was adsorbed to the surface of the catalyst. Then the adsorption of ozone on the surface of the catalyst promoted the ozone decomposition, leading to more active free radicals(not hydroxyl radical) that could efficiently improve the organics removal.