Experimental Study On Pathogenic Microorganisms In Raw Water Disinfected By Hydrodynamic Cavitation Due To Combinations Of Triangular Multi-orifice Plates With Venturi Tubes

Water is an indispensable resource for people’s daily life.The safety of drinking water affects the health of people.With the rapid development of our country’s economy and society,the demand for the quality of drinking water has also been improved.In the traditional drinking water disinfection process,chlorine disinfection is the main method.When disinfection is applied,chlorine and organic matter in water will produce disinfection by-products due to chemical reaction.According to previous studies,the disinfection by-products produced by chlorine disinfection reaction are three(carcinogenic,teratogenic,mutagenic)hazards,which threaten the health of drinking water consumers.As a new technology of drinking water disinfection,cavitation disinfection has potential prospect in the field of drinking water disinfection,because of its characteristics of safety,high efficiency,environmental protection and no disinfection by-products.This paper is based on the triangular orifice plate and Venturi combined hydraulic cavitation device designed by Zhejiang University of Technology Hydrodynamics Laboratory to produce stable cavitation.Dantec three-dimensional particle image velocimetry(PIV)was used to analyze the flow field of combined cavitation and the pressure data of the combined cavitation flow were analyzed by SINOCERA-YE6263 pressure data acquisition system,so as to reveal the mechanism of killing the pathogenic microorganism by hydraulic cavitation.Study on flow characteristics based on the above,the raw water samples with different concentration ratio taken from Shengli River in Hangzhou was used to sterilize pathogenic microorganisms.Escherichia coli and total colony count were chosen as indicator bacteria of pathogenic microorganisms,and counted by agar plating method before and after hydrodynamic cavitation.The effects of the Venturi diffusion angle,the ratio of raw water,the number of orifice and the orifice arrangement on the total number of colonies and the killing rate of Escherichia coli were analyzed.Experimental study shows that :(1)Selecting the appropriate diffusion angle and throat length diameter ratio can increase the turbulence effect of the combination.There is an optimal diffusion ?=4.3°and an appropriate throat length diameter ratio L/R=60 made the shear action between water flow strong,the turbulence more intense and the effect of cavitation better.(2)The killing effects could be improved by increase the number of orifice at the same total area of the orifice.(3)Interlaced arrangement multi-orifice plates have a higher killing rate on pathogenic microorganisms than chessboard arrangement multi-orifice plates.(4)The high concentration of the pathogenic microorganisms water sample can be diluted to make more efficient use of the cavitation effect.Hydraulic cavitation is proved an safe,efficient and novel technology way to kill pathogenic microorganisms without adverse by-products.