Study On The Removal Effect And Mechanism Of E.coli By Photocatalytic Enhanced Hydrodynamic Cavitation

Microbial contamination of water bodies mainly refers to bacteria and other pathogenic bacteria that can cause various diseases in humans,etc.The problem of pathogenic microbial contamination in drinking water is one of the most threatening human health issues currently faced.Domestic sewage containing a large number of disease-causing microorganisms will be directly discharged into the water body,posing a great threat to the safety of the water environment and endangering people’s health.Therefore,the search for a more efficient and energy-saving method to treat pathogenic microorganisms in water has become the focus of current research.In recent years,hydraulic cavitation,an emerging advanced oxidation technology,has been paid attention to by scholars for its advantages of easy operation,wide application and no secondary pollution,and many researchers have devoted themselves to the use of hydraulic cavitation to remove microorganisms from water bodies for the purpose of improving water quality.As the research progressed,it was found that the combination with other advanced oxidation technologies could be used to achieve more efficient disinfection of water bodies,solving the problems of long consumption time and low efficiency of hydraulic cavitation technology alone.Currently,combined technology has become one of the main research tools to improve treatment efficiency.In this study,the effect of combined hydrocavitation and photocatalytic technology on the killing of E.coli is discussed using a homemade combined device,and a comparison with hydrocavitation alone and photocatalytic sterilization alone is performed to determine the enhanced effect of the combined system on sterilization,while the possible sterilization mechanism is speculated based on the relevant characterization analysis,providing a new method for the rapid and effective killing of E.coli in water.（1）Separate hydraulic cavitation sterilization experiments determined that the number of orifices to achieve the most excellent hydraulic cavitation sterilization effect was three orifices,the inlet pressure was 3.0 bar,and the initial bacterial solution showed better sterilization effect when it was in acidic conditions.The presence of CO₃^2-in the ambient water promoted the bactericidal efficiency of E.coli,while the presence of PO₄^3-inhibited the bactericidal efficiency of E.coli,and SO₄^2-showed a promotion at low concentrations and inhibition at high concentrations.The oxidation of·OH was determined to be dominant in the cavitation bactericidal system by free radical capture experiments.Transmission electron microscopy（TEM）observed distortion of the bacteriophage cell morphology and destruction of the internal structure,which may be due to the oxidation of free radicals generated during the cavitation process and the disintegration of the cells due to mechanical effects.（2）Fe/Ti O₂ photocatalysts were prepared by sol-gel method,which had better bactericidal effect compared with pure Ti O₂ and the best effect of killing E.coli when the doping amount was 0.9%.X-ray diffraction（XRD）and UV-vis diffuse reflectance spectroscopy（DRS）analyses were performed to determine the synthesized crystalline form,which achieved a larger range of available light utilization and enhanced photocatalytic activity.Photocatalytic sterilization experiments were conducted using the successfully prepared Fe/Ti O₂ photocatalyst with a doping level of 0.9%.The initial bacterial solution showed higher sterilization efficiency at alkalinity,and it was found that anions in the ambient water would inhibit the sterilization effect to a certain extent,and the oxidation of·O₂^-was confirmed to be dominant in the photocatalytic sterilization system by adding a trapping agent,combined with transmission electron microscopy（TEM）to observe the appearance of pits and pores in the treated cells,which could not maintain their integrity.（3）The combined hydrocavitation and photocatalytic technology was used to remove E.coli from water,and the enhanced bactericidal effect of the combined system compared with the separate system was investigated under different ambient water anions,and more than 95%bactericidal effect could be achieved after 40 min of reaction.The combined system is more favorable to kill E.coli under acidic conditions,and the size of the free radicals involved in the reaction process:·OH>·O₂^->h⁺.The sterilization rate remained at about 95%through three cycles of sterilization experiments,indicating that the catalyst can be reused and has strong economic performance.Combining the scanning electron microscopy（SEM）and transmission electron microscopy（TEM）analysis of the catalyst and E.coli cells before and after the treatment,a synergistic mechanism between the two was proposed to enhance the bactericidal effect.