Study On The Effect And Mechanism Of Hydrodynamic Cavitation And Its Enhancement On The Sterilization Of Escherichia Coli

Many pathogens are often found in natural water bodies,causing terrible diseases such as dysentery,typhoid fever and cholera.Escherichia coli（E.coli）is one of the main pathogenic microorganisms that cause foodborne diseases.Therefore,sterilization technology should be applied to the water treatment process.This article reports the effect of single hydrodynamic cavitation and intensification on the killing of E.coli in water.The effects of inlet pressure,initial concentration of bacterial suspension and several additives on the inactivation of E.coli at different growth stages were studied.At the same time,the influence of free radical scavengers on the survival rate of E.coli was discussed.Scanning electron microscope and transmission electron microscope were used to observe the morphological changes of Escherichia coli before and after treatment.Under optimized experimental conditions,the disinfection effect of Escherichia coli reached 77.78%.The results show that the oxidation of hydroxyl radicals plays a major role in hydrodynamic cavitation disinfection.Under the same concentration of hydrodynamic cavitation,E.coli in logarithmic growth phase is more sensitive than E.coli in delayed and stable growth phases.Subsequently,three oxidants,H₂O₂,K₂S₂O₈and Na Cl O,were added to explore the disinfection effect under their single action and combined hydrodynamic cavitation action,and the synergistic effect was inferred.This article puts forward some suggestions on the practical application of hydrodynamic cavitation disinfection.The main research contents are as follows:（1）Through experimental research,when the number of cycles is 5 and the inlet pressure is 3.0 bar and the E.coli suspension concentration is 10⁷CFU/m L and E.coli is in the logarithmic growth phase,the response to hydrodynamic cavitation is the best,which reaches 77.78%.In the experiment of free radical scavenger,the addition of hydroxyl free radicals and superoxide free radicals reduced the cavitation effect.（2）At the same time,this study characterize and analyze the E.coli by SEM and TEM before and after disinfection of hydrodynamic cavitation,and explore the specific damage sites of microbes.The results show that the thermal and mechanical produced by the hydrodynamic cavitation process caused the deformation of some bacterial cells.The intense shock waves propagating in the liquid are also responsible for the accumulation of substances in the cytoplasm.Fast-speed shock waves and local high hot spots in hydrodynamic cavitation are also responsible for the holes in bacterial cell membrane seen in SEM and TEM photos.As the cavitation intensity increases,the length of the bacteria gradually increases.Eventually the bacteria break.It may be due to the local high pressure generated in the process of hydrodynamic cavitation.Excessive pressure makes the bacteria elongate.And uneven pressure leads to the breakage of bacterial cells.The local hot spots generated during the cavitation process will also cause irreversible damage to the DNA and proteins in the bacterial cells,thereby affecting the subsequent reproduction of E.coli.The destruction of cells in the process of hydrodynamic cavitation can also be attributed to the hydroxyl free radicals and hydrogen free radicals generated during the cavitation process,which leads to oxidative damage of bacterial cells.The oxidation of strong oxidizing free radicals affects important components of microorganisms,such as proteins,lipids,DNA and polysaccharides.Hydroxyl free radicals can attack and oxidize double bonds and sulfhydryl groups in protein components,and cause oxidative stress,and produce irreversible damage to microorganisms.This will cause damage to the bacterial cell membrane and genetic material.（3）When the three oxidants combined with hydrodynamic cavitation disinfection methods reach a certain removal amount,the time required is significantly shorter than the single hydrodynamic cavitation disinfection and the single oxidant disinfection.All this shows that when hydrodynamic cavitation and three oxidants are combined to disinfect E.coli,the two strengthen each other and have a synergistic effect.The addition of H₂O₂,K₂S₂O₈and Na Cl O increases the gas nucleus content in the water,reduces the difficulty of cavitation,and enhances the cavitation effect.At the same time,the extreme environment formed by cavitation strengthens H₂O₂,K₂S₂O₈and Na Cl O.The two strengthen each other to remove E.coli in the water and promote the oxidative inactivation of E.coli in the sewage.