Construction Of Hydrodynamic Cavitation Combined With Advanced Oxidation Technologies And Degradation Of Organic Pollutants

In recent years,with the rapid development of modern industrial technology,a lot of organic pollutants are discharged into the environment.At the same time,the refractory substances in the water body are more and more complex.Some traditional methods cannot completely degrade these pollutants.Therefore,it is urgent to explore some new sewage treatment technologies to satisfy the requirements of industrial development and environmental protection.The advanced oxidation technology is a potentially advantageous technology for treatment of complex industrial wastewater,which produces highly active free radicals and oxidizes refractory organic pollutants.The hydrodynamic cavitation is a new advanced oxidation technology,which has many advantages,such as simple equipment,no secondary pollution,easy realization and maintenance,etc.It is still at the initial stage in the field of environmental treatment.However,the efficiency of hydrodynamic cavitation treatment alone is low and organic pollutants cannot be degraded completely.Therefore,the combination of hydrodynamic cavitation technology and other advanced oxidation technology may be a better solution to solve this problem.In addition,hydrodynamic cavitation technology can be applied in a broader field.In this paper,a new hydrodynamic cavitation degradation system is constructed in the laboratory.Hydrodynamic cavitation catalysis,hydrodynamic cavitation combined with photocatalysis and hydrodynamic-ultrasonic double cavitation are studied to optimize the cavitation effect.Some venturi tube geometries such as shape and size,divergence angle and length of the venturi tube throat are included.In addition,the optimal degradation conditions of each system are tested by operating parameters of hydrodynamic cavitation,including inlet pressure,operating temperature,initial concentration of pollutants,pH value and so on.Because cavitation can produce extreme conditions,it can stimulate catalyst with suitable bandwidth and further improve the degradation efficiency of organic pollutant on hydrodynamic cavitation with other advanced oxidation technologies.Many catalysts for different cavitation system were designed and prepared to ensure the stability of the catalysts for the extreme conditions caused by cavitation.In addition,the magnetic catalyst can be reused to achieve the concept of green environmental protection.Moreover,the shock wave and shear force produced by hydrodynamic cavitation can clean the surface of the catalyst.These can avoid the adsorption of pollutants on the surface of the catalyst and make more active sites applied in wastewater treatment.The specific content of the study is as follows:?1?A new method of hydrodynamic cavitation catalysis was studied.Fe³⁺-doped TiO₂ catalyst was prepared by sol-gel method and was successfully used in the hydrodynamic cavitation system to degrade Rhodamine B?RhB?.The crystal form,morphology,structure,chemical composition and absorption range of the prepared TiO₂ and Fe³⁺-doped TiO₂ with different Ti/Fe mole ratio were studied.Many methods of X-ray diffraction?XRD?,scanning/transmission electron microscope?SEM/TEM?,X-ray photoelectron spectroscopy?XPS?,ultraviolet-visible diffuse reflectance spectroscopy?UV-vis DRS?and photoluminescence?PL?were used for the characterization.The influences of throat shape and size of venturi tube and throat divergence angle on hydrodynamic cavitation were investigated.The effects of Fe³⁺-doped TiO₂ catalyst with different Ti/Fe mole ratio on the degradation of RhB were studied.In addition,the operating parameters of hydrodynamic cavitation were optimized by response surface methodology,including the effects of inlet pressure,operating temperature and initial concentration of RhB on the hydrodynamic cavitation degradation of RhB.Finally,the possible mechanism of catalytic degradation of RhB by hydrodynamic cavitation in the presence of Fe³⁺-doped TiO₂was proposed.The results show that the catalytic degradation ratio of RhB is 91.11%under the optimal experimental conditions.?2?A new type of hydrodynamic cavitation combined with photocatalysis system was constructed.The magnetic coated Fe₃O₄@TiO₂-Pd catalyst was prepared to degrade Crystal Violet?CV?.The crystal structure,chemical composition,morphology,absorption range and recovery magnetic properties of Fe₃O₄@TiO₂-Pd catalysts with different thickness of TiO₂ shells were investigated by various characterization techniques.The effects of throat length of venturi tube and inlet pressure on the degradation of CV by hydrodynamic cavitation were investigated.The effects of inlet pressure,different catalysts and different combination methods degradation of CV on hydrodynamic cavitation combined with photocatalytic system were studied.The reactive oxygen species?ROS?were identified by using different trapping agents.Finally,the possible mechanism of hydrodynamic cavitation combined with photocatalysis degradation of CV in the presence of magnetic coated Fe₃O₄@TiO₂-Pd was proposed.The results show that the hydrodynamic cavitation combined with photocatalysis degradation of CV can reach 82.17%in the presence of Fe₃O₄@TiO₂-Pd.?3?The magnetic integrated Zn_0.5Co_0.5Fe₂O₄ catalyst was prepared and a newly hydrodynamic-ultrasonic dual-cavitation system was assembled to degrade Acid Orange II?AO II?.The crystal structure,morphology and chemical composition of Zn_0.5Co_0.5Fe₂O₄ were investigated by various characterization techniques.The effects of inlet pressure and ultrasonic power on the degradation of AO II by hydrodynamic-ultrasonic dual-cavitation were investigated.In addition,the different methods were studied and the composite effect of the composite technique was calculated.Finally,reactive oxygen species?ROS?in the degradation process of AO II were identified,and the possible mechanism of degradation of AO II in the presence of magnetic catalyst Zn_0.5Co_0.5Fe₂O₄ was proposed.The experimental results show that the degradation ratio of AO II can reach 84.42%in the presence of Zn0.5Co0.5Fe2O4.