Experimental Study On Degradation Of Refractory Wastewater By Hydrodynamic Cavitation Due To Venturi Tube And Triangular Multi-Orifice Plates And The Cavitation Turbulence Characteristics

With the rapid development of economy and society in China,water pollution was increasingly serious,and thus directly affected the life quality of human beings.Generally,water pollution could be divided into two major categories: domestic sewage and industrial wastewater.For domestic sewage,conventional wastewater treatments such as physical methods,chemical methods and biological methods have been extensively applied.However,for the industrial wastewater,especially for the organic wastewater which containing toxic refractory pollutants,traditional waste water treatments could not meet the requirements of processing emissions.Hydrodynamic cavitation technology as a new processing method,not only could effectively degrade persistent organic pollutants,but also been of the advantages of efficient,economic,energy-saving and no secondary pollution,etc.The application of hydrodynamic cavitation technology had become a research focus in the field of water pollution control technology.Meanwhile,cavitation is a complex phenomenon be of micro and randomin fluid,the degradation mechanism of hydrodynamic cavitation had been a scientific research difficulties.This thesis was based on the self-developed hydrodynamic cavitation reactors composed of the Venturi tube with triangular multi-orifice plates,could been concluded two main parts: firstly,the refractory wastewater has been degraded due to hydrodynamic cavitation to optimize the geometric parameters of cavitation reactors and the operating condition during the experiments.Then,cavitation turbulence characteristics has been studied to reveal of the degradation mechanism of hydrodynamic cavitation.The specific contents were as follow:(1)The Venturi tube was utilized as the hydrodynamic cavitation reactor,and nitrobenzene was chosen as the refractory hydrophobic pollutant,the effect of various parameters such as the throat length of the Venturi tube,throat velocity,initial concentration of nitrobenzene and the pH value on the degradation of refractory hydrophobic pollutants were investigated.(2)The triangular multi-orifice plates were used as the hydrodynamic cavitation reactor,and p-nitrophenol was chosen as the refractory hydrophilic pollutant,the effect of orifice flow velocity,orifice numbers,orifice sizes,initial concentrations of p-nitrophenol and cavitation number on the degradation rates of refractory hydrophilic pollutants were measured.(3)Different combinations of the Venturi tubes with triangular multi-orifice plates were composed as the hydrodynamic cavitation reactor.The different combination forms,flow velocity,treatment time and initial concentrations of pollutants were varied to measure the effects on the degradation rates of the hydrophilic and hydrophobic mixtures,and the experiment gave the optimal combination form.(4)The pressure characteristics on the throat of the Venturi tube andbehind multi-orifice plates were experimental studied by the pressure data acquisition system of SINOCERA-YE6263.The effect of the throat length due to the Venturi tube,multi-orifice plates with different size,number and arrangement on the time average pressure,frequency spectrum and auto-correlation function were considered.(5)The practical chemical wastewater was treated due to the combination of the Venturi tube with triangular multi-orifice plates.The COD value was chosen as the detection index and the effect of combination forms,orifice numbers and sizes,initial concentrations of chemical wastewater,treatment time,cavitation number and pH value on the degradation rates were studied.And the optimal parameters of combination forms and the operating conditions have been provided.(6)In order to analyze the turbulence characteristics in cavitation flow field and reveal the degradation mechanism of hydrodynamic cavitation,time-averaged velocity,turbulence intensity and turbulent shear stress behind the different multi-orifice plates were measured by the advanced test instruments,that were,the three-dimensional particle image velocimetry(PIV)and the high-speed photography.