Preparation And Characterization Of CoMnAl Composite Heterogeneous Fenton-like Catalyst And Its Performance For Pretreatment Of Pharmaceutical Wastewater

In recent years,pharmaceutical manufacturing industry has developed rapidly in China,and the discharge amount of wastewater has been improved continuously.Thereinto,the composition of synthetic pharmaceutical wastewater is the most complex,with high content of hard-biodegraded substances,high salt content and poor biodegradability,and the high efficienct and stable treatment of synthetic pharmaceutical wastewater is difficult.Fenton oxidation has been used widely in pretreatment of pharmaceutical wastewater and other refractory wastewaters,but there are still some problems,such as need of harsh pH condition,high dosage of chemicals and high production of iron sludge.Because of the low production of iron sludge and recyclable reproducibility of catalyst,heterogeneous Fenton-like reaction has become a hot research and development technology for pretreatment of refractory wastewater.In this thesis,the synthetic pharmaceutical industrial wastewater was the treatment object,the preparation condition of CoMnAl-CMO-Al₂O₃ composite heterogeneous Fenton-like catalyst was optimized,K-doped modification of the catalyst and its performance were explored.themethods to improve the catalyst activity,the heterogeneous Fenton-like reaction of for treating the actual synthetic pharmaceutical wastewater.The mechanism of heterogeneous Fenton-like reaction of the catalyst was preliminarily revealed,and a efficient and stable heterogeneous Fenton-like pretreatment process for pharmaceutical wastewater was developed.The major results are as follows:1. The heterogeneous Fenton-like catalyst was prepared by CoMnAl composite metal oxides supported on Al₂O₃,and the optimized preparation conditions were obtained through the response surface experiment design analysis and fitting the quadratic regression equation:the concentrations of aluminum nitrate,manganese nitrate and cobalt nitrate were 60 g/L,5 g/L and 4 g/L in the nitrate immersion liquid respectively,and the temperature of impregnation and calcination were set at 40°C and500°C,respectively.The prepared catalyst CoMnAl-CMO-Al₂O₃ had a huge pore volume and good adsorption performance,and the crystal form of the catalyst was mostly spinel phase with Co and Mn elements.It lays a foundation for single electron transfer and Fenton catalytic internal circulation?Mainly between Co and Mn elements?.2. The synthetic pharmaceutical wastewater was pretreated by heterogeneous Fenton-like catalytic reaction,and the effect was verified at different pH,H₂O₂ dosage and other factors.Results showed that the prepared catalyst CoMnAl-CMO-Al₂O₃ had a high catalytic oxidation performance in the pH range of 3-10,and the TOC removal efficiency of pharmaceutical wastewater reached 35±2%and B/C was increased from0.173 to above 0.4.The repeated experiment results showed that the surface composition of the catalyst did not change significantly after five cycles,and the TOC removal efficiency of pharmaceutical wastewater remained around 34%after regeneration,which showed a good stability and application potential.3. Effects of different calcination methods on the surface characteristic of catalysts were analyzed.Results showed that the CoMnAl-CMO-Al₂O₃-carb catalyst which was prepared by NH₄HCO₃ calcination method had the largest specific surface area of 230m²/g and the highest catalyst activity,and the surface crystal structure and element valence of the catalyst were consistent with unmodified catalyst.The catalyst was further modified by impregnated with different concentrations of KNO₃ solution,the surface of the catalyst formed birnessite and KNO₃ crystals.Results showed that the activity of CoMnAl?K?-CMO-Al₂O₃-carb catalyst was further enhanced when the concentration of KNO₃ solution was 0.5 mol/L,and the TOC removal efficiency of synthetic pharmaceutical wastewater reached 44.2±1.5%.4. The heterogeneous Fenton-like catalytic reactor with continuous operation was designed,the optimized pretreatment process parameters of synthetic industrial pharmaceutical wastewater was obtained:the reaction time was 6 h,and the ratio of H₂O₂ to catalyst was 1.2-1.4 m L H₂O₂/g catalyst.When pH was at a range of 7-9,and the TOC of influent were 750±20 mg/L?The loading was 3±0.08 kg/?m³·d??and2150±50 mg/L?The loading was 8.6±0.2 kg/?m³·d??,the removal efficiency of TOC remained above 17%and 20%,respectively,and the B/C both reached above 0.35 after one week of operation.The reagent cost and solid waste production were reduced compared with homogeneous Fenton.The prepared CoMnAl?K?-CMO-Al₂O₃-carb heterogeneous Fenton-like catalyst had the characteristics of a wide pH adaptation range,good stability and reproducibility.It is excepted to provide a new solution for the pretreatment of synthetic pharmaceutical wastewater.