Experimental Study Of Pathogenic Microorganisms In Raw Water Killed By Hydrodynamic Cavitation Due To Combinations Of Square Multi-orifice Plates And Venturi Tubes

The safety of drinking water is directly related to the survival of human beings,It is the necessary elements of social and economic development and the continuous progress of human civilization as an important resource.Chlorination disinfection is used by Waterworks as the most commonly disinfection methods.Chlorine has a good oxidation performance,convenience of storage,easy to use and so on,these advantages of chlorination disinfection is widely recognized.However,in recent years,The various disadvantages of chlorination disinfection are proved,chlorine disinfection process often produce a number of by-products(THMs?HAAs etc.),These by-products pose a great threat to human health.The hydraulic cavitation disinfection technology discussed in this paper has characteristics of no disinfection by-products,high efficiency and low energy consumption,it has been paid more and more attention by scholars.Based on the self-developed hydrodynamic cavitation reaction device,Escherichia coli and total colony count in non-potable water source were chosen as the indicator bacteria to study effects of cavitation number,throat velocity,arrangement of orifice,initial concentration of raw water,and cavitation time on inactivation rates of Escherichia coli and total colony count by the different combinations of multi-orifice plate,Venturi throat and Venturi diffusion angles.The advanced three-dimensional particle image velocimetry(PIV)was used to analyze the flow characteristics of porous plate,and the distribution of velocity,turbulent intensity and Reynolds stress were obtained.The fluctuation degree of flow velocity?turbulent intensity? Reynolds stress that combined form A1(throat length of 300 mm,diffusion angle of 4.3°)and A2(throat length of 300 mm,diffusion angle of 5.7°)are obviously greater than A3(throat length of 150 mm,diffusion angle of 4.3°)? A4(throat length of 150 mm,diffusion angle of 5.7°)venturi tube combination.The YE6263 pressure data acquisition system was used to collect the pulsating pressure of working section.The two times significant drop in pressure in operation of combined hydraulic cavitation promote cavitation.Under the condition of double pump,the cavitation number of porous plate?throat and diffusion segment is much smaller than the condition of single pump,so the cavitation effect of double pump is much better than single pump.The total colony and Escherichia coli were selected as the index,the raw water in Shengli River of Hangzhou was treated with different initial concentrations,and the killing rate of Escherichia coli was detected by agar plate counting method.The experimental results showed that the optimal inactivation effect was achieved as the combined form was staggered 25-orifice multi-orifice plate,throat length of 300 mm and diffusion angle of 4.3°.At the same time,reducing the cavitation number,increasing the throat velocity,prolonging the cavitation time and selecting the proper initial concentration of raw water would contribute to improve the inactivation effects of Escherichia coli and total colony count.