Study On Heterogeneous Catalytic Oxidation System Under Neutral Condition In Wastewater Treatment

The heterogeneous catalytic oxidation system under neutral condition is of great significance for the treatment of refractory wastewater. For one thing, use of heterogeneous catalysts reduces the loss of metal ions and lows solid waste production. For another thing, the optimum reaction pH range is broadened, especially better performance at neutral pH values. Wastewater after treatment could be discharged directly without pH adjustment, lowing the production cost. Based on the surface adsorption-catalytic oxidation mechanism, the degradation-resistant wastewater containing complexing agent EDTANa2 or the cationic reactive dye MB is degraded effectively with highly reactive Fe3O4 nano-particles synthesized or Ti ion successfully doped Fe2.5Ti0.5O4 catalysts. The reactive radicals are usually less reactive at the heterogeneous catalytic oxidation system under neutral condition. Phenol can hardly be degraded for the quenching effect on the HO radical. With addition of O3, the aromatic compounds such as phenol can be mineralized well in the catalytic oxidation system. There is a synergistic effect between the O3 and the H2O2-Fe3O4/SiO2 systems. The cost of complete mineralization of organics by chemical oxidation is usually high. The discharge after moderate oxidation by the heterogeneous catalytic oxidation system under neutral condition could be further treated directly with improved biodegradability. This combination technology of chemical oxidation and biological oxidation is an economical and effective wastewater treatment method.Main contents and conclusions are included in the following three parts:1The active Fe3O4 nano-particles were synthesized by the modified Massart’s menthod. With complexing agent EDTANa2 as a model compound, the COD removal rate at the H2O2-Fe3O4 oxidation system under neutral condition was equal to that at pH 3 for Fenton reaction. The surface adsorption-catalytic oxidation mechanism was testified, besides, the oxidation process was promoted by the adsorption process. The reactive intermediates HO was trapped by the electron spin resonce and the HO produced at the surface of the catalysts was responsible for the mineralization of EDTANa2.2Ti ion was introduced into the Fe3O4 nanao-particles structure by isomorphous replacement to improve the activety of the catalyst. Effect of different Ti ion doping amount of Fe/Ti catalysts was investigated and the optimal doped catalyst was selected as Fe2.5Ti0.5O4. The cationic reactive dye MB was not degraded well by the H2O2-Fe3O4 system for the weak adsorption. The same COD removal efficiency of MB solution catalyzed by the H2O2-Fe2.5Ti0.5O4 system at neutral pH value was achieved as the Fenton reaction at pH 3. The kinetic study showed that the detradation of MB followed the first order kinetic rate law and the production rate of HO on the catalyst surface controled the reaction process. The catalytic efficiency was regenerated after degradation of organic adsorpted on the catalyst surface by O3. Further, the reaction rate was accelerated by the O3-Fe2.5Ti0.5O4 catalytic oxidation system to degrade the MB solution and the catalyst recycling efficiency performed better than the H2O2-Fe2.5Ti0.5O4 system.3Phenol was hardly degraded by H2O2 at neutral pH values even at the presence of catalysts. Because phenol had quenching effect on HO and the HO produced on the catalyst surface was always less reactive. It was easily quenched before reaction with phenol and resulted in poorer degradation efficiency. As SiO2 was preferable for the stability of HO, the activity was improved by loading Fe3O4 on amorphous SiO2 by the adsorption-coprecipitation-calcination preparation method. Further, phenol could be well degradated by the O3-Fe3O4/SiO2-H2O2 oxidation system under neutral condition for the synergy effect between O3 only and the H2O2-Fe3O4/SiO2 systems. The degradation products were analysed by HPLC method and the mechanism of phenol degradation by HO was inferred. What’s more, the biochemical oxygen demand (BOD) of the solution was monitored at different oxidation time by system. It was preferred to improve the biodegradability of the solution after moderate chemical oxidation. The combined technology of chemical and biological oxidation process was studied preliminarily. And it laid a foundation for the treatment of practical industrial wastewater economicly and effectively.