Study On The Killing Effect Of Hydraulic Cavitation On Escherichia Coli

Water is the basic material base that sustains human beings and all natural creatures.The safety of drinking water is related to the survival of human beings.80% of the world’s diseases are related to pathogens in water.In recent years,the outbreak of disease events due to microbial pollution emerge in endlessly.As a newly emerging technology,hydraulic cavitation has gradually come into people’s sight in recent years.Due to its characteristics of no secondary pollution,simple equipment,and simultaneous treatment of a large amount of sewage,some scholars have gradually applied it to water disinfection treatment.At present,many scholars in China have devoted themselves to the study of hydraulic cavitation technology.This paper reports the killing effect of hydraulic cavitation on Escherichia coli in water.Firstly,the effect of geometric parameters of orifice plate on killing Escherichia coli by hydraulic cavitation was studied.Secondly,the effect of operating conditions on the killing rate of Escherichia coli was studied,and the effect of free radical trapping agent on the sterilization of hydraulic cavitation system was explored.Finally,the possible sterilizing mechanism was deduced based on the changes of Escherichia coli morphology observed by scanning electron microscope（SEM）before and after treatment.（1）Orifice plates with different geometric parameters were used as hydraulic cavitation reactors to kill and treat the wastewater containing Escherichia coli and determine the optimal geometric parameters of orifice plates to ensure that the orifice plates with the strongest cavitation degree were used as hydraulic cavitation reactors in subsequent experiments.The experimental results show that when the number of orifices is 3,the orifice diameter is 2.00 mm,and the orifice thickness is 4.00 mm,the orifice plate with staggered distribution has the strongest hydraulic cavitation effect.（2）Using the optimal geometric parameters of orifice plate as a hydraulic cavitation reactor to kill the E.coli,studies and analyzes the cavitation time,inlet pressure,Escherichia coli,initial concentration,initial p H,inorganic anion etc.The influence of operating conditions on the E.coli bacteria killing rate,further optimize the hydraulic cavitation sterilization conditions.It was found that the killing rate of Escherichia coli increased with the prolongation of cavitation time.When other operating conditions are the same,the higher the inlet pressure,the better the killing effect of E.coli.The lower the initial concentration of E.coli,the better the killing effect;In acidic condition,Escherichia coli had the best killing effect and was better than neutral condition and alkaline condition.The presence of inorganic anions can weaken the killing effect of hydraulic cavitation system on Escherichia coli and inhibit it.In the free radical capture experiment,the hydraulic cavitation sterilization process hydroxyl radicals and superoxide radicals work simultaneously,but mainly due to the strong oxidation of hydroxyl radicals.（3）Escherichia coli before and after hydraulic cavitation was observed and analyzed by SEM.Due to mechanical and thermal effects in the process of hydraulic cavitation,deformation of Escherichia coli bacteria can be observed.The surface and edge of the bacteria are significantly distorted,and holes can be obviously seen on the surface of the bacteria.As the thalli were repeatedly exposed to the oscillating cavity,the disintegrated cell fragments could be clearly observed when different scales were selected for observation.The cell structure was no longer complete,and the contents leaked out and wrapped most of the cell fragments and only a small amount of demorphthalli.In this case,the disintegration of most bacterial cells will inevitably lead to the death of Escherichia coli,so as to achieve the effect of killing Escherichia coli.