Construction Of A New Orifice Hydrodynamic Cavitation System And Study On Degradation Of Antibiotics

Antibiotics are a kind of common antibiotics,which are widely used in medical treatment,animal husbandry and breeding.In recent years,with the increase of market demand,the production of antibiotics is also increasing.At the same time,it is also accompanied by the treatment of high concentration antibiotic wastewater in the process of production and use.Usually,antibiotics are difficult to be degraded due to their complex structure and stable properties,which undoubtedly brings great difficulties to the use of traditional water treatment methods.Therefore,it is important to find a new and effective method and technology for the treatment of antibiotic wastewater.As a kind of advanced oxidation technology with simple equipment and no secondary pollution,hydrodynamic cavitation has been widely concerned by researchers.In this work,the geometric parameters of the orifice plate and the operating conditions of the degradation experiment were investigated,and the device parameters of the hydrodynamic cavitation system were optimized.The combination of hydrodynamic cavitation and other advanced oxidation technologies was explored.It is of great significance and value to develop efficient wastewater treatment technology and process.In the first part,the effects of different orifice plate geometric parameters such as orifice shape(circle,square and triangle),orifice plate thickness(2.00-6.00 mm),orifice number(n=1-5)and orifice divergence angle(?=0°and±45°)on the norfloxacin degradation by using hydrodynamic cavitation were studied to obtain a strong hydrodynamic cavitation effect.And the effects of various operating parameters such as solution p H(3.0-9.0)and initial norfloxacin concentrations(5.0-15 mg/L)on the norfloxacin degradation by using hydrodynamic cavitation were discussed.The trapping experiments of free radicals(·OH and·O₂^-)were also carried out for exploring the mechanism of norfloxacin degradation.In addition,adopting the designed orifice plates with optimized geometric parameters,the norfloxacin degradation efficiencies by using hydrodynamic cavitation combined with some added oxidants(H₂O₂,K₂S₂O₈and Na Cl O)were investigated.The Total Organic Carbon(TOC)analysis at the optimum conditions was also performed to identify the mineralization extent.The intermediate products during the norfloxacin degradation were detected by using Liquid Chromatograph-Mass Spectrometer(LC-MS).The experimental results indicated that,under 5.0 bar inlet pressure for 10 mg/L initial norfloxacin concentration at 40°C operating temperature in p H=3.0 solution,the degradation ratio of norfloxacin can reach up to 84.20%in the hydrodynamic cavitation system and can reach up to 96.45%in the hydrodynamic cavitation+H₂O₂system by using the orifice plate with 4.00 mm thickness,three square orifices and?=0°orifice divergence angle.The TOC test results show that the mineralization ratio can reach 71.57%in the hydrodynamic cavitation system for 150min successive cycling,which demonstrated that the hydrodynamic cavitation can effectively mineralize norfloxacin.In addition,the LC-MS results manifested that norfloxacin molecules can be degraded into a series of intermediate products with low molecular weight and further be oxidized into CO₂,H₂O and some inorganic ions during the hydrodynamic cavitation process.Overall,the work has demonstrated that the hydrodynamic cavitation is an effective strategy for a large-scale treatment of antibiotics wastewater.In the second part,the degradation of chlortetracycline in aqueous solution is performed by using an improved hydrodynamic cavitation device with expanded orifice plate.Different device parameters in the improved hydrodynamic cavitation device such as the diameter(X)of orifice distribution region,the length(Y)of orifice plate inlet region and the length(Z)of orifice plate outlet region are optimized.The influences of operating parameters including inlet pressure,solution p H and initial chlortetracycline concentration on the hydrodynamic cavitation degradation of chlortetracycline are investigated by response surface methodology(RSM).Besides,the effects of inorganic anions,metal ions and added H₂O₂on the degradation of chlortetracycline by using hydrodynamic cavitation are explored.The formed intermediate products during the chlortetracycline degradation are detected.The experimental results indicated that,for optimized device parameters(X=32 mm,Y=100 mm and Z=200 mm),the degradation ratios can reach 78.53%and 94.65%,respectively,in hydrodynamic cavitation and hydrodynamic cavitation+H₂O₂systems under 3.0 bar inlet pressure,10mg/L initial chlortetracycline concentration and p H=7.0.And the mineralization ratio can reach 60.77%in the hydrodynamic cavitation+H₂O₂system for 60 min treatment time,demonstrating that chlortetracycline can be mineralized effectively.The existences of the inorganic anions and the metal ions show inhibition influences for the chlortetracycline degradation reactions by using hydrodynamic cavitation.In addition,the LC-MS results manifested that chlortetracycline molecules can be degraded into a series of organic compounds with low molecular weight and further be oxidized into CO₂,H₂O and some inorganic ions with the extension of treatment time in the hydrodynamic cavitation+H₂O₂system.Overall,the work has revealed that the hydrodynamic cavitation is a potential technology for a large-scale treatment of antibiotics contaminated water.In the third part,a novel magnetic Z-scheme(TiO₂/Er³⁺:YAlO₃)/Ni Fe₂O₄photocatalyst was prepared and then a combined system of hydrodynamic cavitation(hydrodynamic cavitation)and photocatalysis was constructed for effective degradation of oxytetracycline in wastewater.The crystal structure,chemical composition,morphology and optical property of the prepared Z-scheme(TiO₂/Er³⁺:YAlO₃)/Ni Fe₂O₄photocatalyst were investigated by using corresponding characterization techniques(XRD,SEM,EDX-Mapping,TEM,EDX,XPS,DRS and PL).Moreover,the degradation efficiency of oxytetracycline by using the combined system of hydrodynamic cavitation and photocatalysis in the presence of different photocatalysts was compared.The effect of initial oxytetracycline concentrations on the degradation of oxytetracycline was also considered.The degradation ratio of oxytetracycline can reach84.45%in the combined system of hydrodynamic cavitation and photocatalysis in the presence of Z-scheme(TiO₂/Er³⁺:YAlO₃)/Ni Fe₂O₄photocatalyst for continuous cycling90 min,which is much higher than that(33.99%)in hydrodynamic cavitation system alone.The trapping experiments of free radicals were also carried out for exploring the mechanism of oxytetracycline degradation.Finally,the possible mechanism of photocatalysis intensifying hydrodynamic cavitation degradation of oxytetracycline in the presence of magnetic Z-scheme(TiO₂/Er³⁺:YAlO₃)/Ni Fe₂O₄photocatalyst was proposed.