A Study On The Characteristics And Application Of Catalytic Oxidation Of Water Pollutants

Catalytic oxidation technology has attracted much attention in recent years due to its ability to efficiently remove organic matter from water.It is an oxidation technology involving hydroxyl radicals（·OH）,and ·OH has high oxidizability.Many researchers have used catalytic oxidation technology of hydrogen peroxide-based for organic matter degradation,but there are few reports on catalytic oxidation to remove ammonia nitrogen.In the study,effects of oxidation by hydrogen peroxide,hydrogen peroxide oxidation catalyzed by iron and oxidation catalyzed by aluminum on aquatic organic matter（AOM）were studied by using three-dimensional fluorescence and ultraviolet differential absorbance techniques.Influence of above oxidation on structure and disinfection by-products formation potential of dissolved organic matter（DOM）was analyzed.On the other hand,magnetic MgO-Fe₂O₃ was prepared by coprecipitation method and applied to ammonia nitrogen（NH₄⁺-N）degradation in winter.At low temperature（10℃）,the effects of ozonation and MgO-Fe₂O₃ catalyzed ozonation of ammonia nitrogen were systematically investigated.The physical properties of the catalyst and the catalytic performance of NH₄⁺-N degradation were analyzed,and the mechanism of catalytic oxidation for ammonia degradation was discussed.Results showed that iron and aluminum obviously catalyze the oxidation of organic matter by hydrogen peroxide,and the catalytic ability of iron is stronger than that of aluminum.When the dosage of catalyst and H₂O₂ were0.018 mmol·L^-1,and 3.5 mg·L^-1 respectively,the removal rates of UV254 and TOC were 35.5%,36.4% respectively for iron catalysis and 5.0%,29.3% for aluminum catalysis,while only 14.0%,16.7% for oxidation by hydrogen peroxide.Three-dimensional fluorescence spectroscopy and UV differential absorbance deconvolution integral were used to detect the differences of the three kinds of oxidation for the structure of organic matter.Catalytic oxidation had no effect on the position of the fluorescence peak,while theintensity of fluorescence peak and the integral value of regional fluorescence were to some extent weakened.Among them,iron catalysis had higher degree of degradation for the protein-like region,fulvic-like acid of visible region and fulvic-like acid of ultraviolet region.According to the UV differential deconvolution,it can be obtained that sites damaged by three kinds of system were consistent for organic matter in water at 272 nm,but the degree of damage was different.For example,while the doses of catalyst and H₂O₂ were 0.018 mmol·L^-1,and 3.5 mg·L^-1 respectively,the difference in UV absorbance ΔA₂₇₂ / A₂₇₂ was 7.0% for oxidation by hydrogen peroxide,8.3%for aluminum catalysis and 18.9% for iron catalysis,respectively.The removal rate of trihalomethane was increased by iron and aluminum catalysis oxidation,and the removal rate of aluminum catalysis was better than that of iron catalysis.The presence of MgO-Fe₂O₃ significantly improved the efficiency of NH₄⁺-N ozonation,e.g.from 0.243 mg/（L·min）by single ozonation to 0.761mg/（L·min）by MgO-Fe₂O₃（nMgO: nFe₂O₃=1:2）under the same p H（8.8）.Fourier transform infrared（FT-IR）results confirmed with XRD findings,illustrating that disordered iron magnesium ore（MgFe₃O₄ and Fe Mg（OH）₂）were formed in magnetic MgO-Fe₂O₃.The selectivity to gaseous products（STG）increased and the removal rate of ammonia（RRA）decreased with the increase of iron content in MgO-Fe₂O₃.Especially,MgO-Fe₂O₃（nMgO:n Fe₂O₃=1:2）exhibited good catalytic that the STG and RRA achieved 40% and50% respectively,when p H was 8.8 after 60 min.What is more,80% removal rate was presented at 120 min.There were at least two roles the catalyst played.Firstly,the catalyst maintained a higher p H of the system,increasing the fraction of NH₃ and promoting the reaction between O₃ and NH₃.Secondly,the catalyst enhanced the production of ·OH by O₃ catalytic decomposition,which accelerated ozonation of ammonia adsorbed on the surface.p H effects were dominated for NH₄⁺-N degradation and ·OH did participate in the reaction as an evidence of the effects of tert butyl alcohol（TBA）and chloride ion（Cl^-）.Introduction of Cl^-significantly accelerated thereaction rate of catalytic oxidation with MgO-Fe₂O₃.It is easily separated from the reaction solution and recycled because of the magnetic properties of MgO-Fe₂O₃.