Theoretical And Experimental Investigation Of Organic Sewage Degradation Using Hydrodynamic Cavitation

With the continuous development of modern industry,such as pharmaceutical chemical,printing and dyeing industry,there are increasing amount of synthetic macromolecules and refractory chemicals in wastewater.The traditional wastewater treatment methods cannot meet the increasingly stringent environmental requirements,and it is very urgent to research and develop the new-type wastewater treatment method and technological process.Hydrodynamic cavitation,as an advanced oxidation process with advantages of simple reactor design and no secondary pollution,becomes a hotspot for scholars from various countries.By combining theoretical analysis with experimental study,this paper deals with the basic and key scientific problems of hydrodynamic cavitation applying to organic sewage treatment.The results of the study have important academic significance and practical value for developing the wastewater treatment technique with our independent intellectual property rights.In theoretical research,by comprehensively taking the effects of heat conduction,diffusion of molecules and ions and chemical reactions into consideration,a single bubble dynamic model is built to capture the dynamic characteristics of cavitation bubbles and to analyze the chemical reactions inside bubble.The degradation mechanism of organic matter in hydrodynamic cavitation process is revealed.The influence rules of initial bubble radius,upstream inlet pressure,downstream recovery pressure and geometrical parameters of orifice plate are explained.Then,considering the distribution of gas nucleus radius and the cavitation event rate,a model for predicting the free radicals yield during the entire lifetime of bubble cluster is also developed.The reliability of the model is verified from the perspective of operating and geometrical parameters.Based on the fitting of the massive calculation data,a correlation for calculating the average hydroxyl yield in the cavitation field is proposed,which is helpful to optimize operating conditions and cavitation induced structures in wastewater treatment.The correlation also provides guidance for the amplifier design of cavitation reactors.Based on the theoretical results,73 reversible chemical reactions and 26 reagents are detected.Among the strong oxidizing components,·OH takes the largest proportion and hence the oxidation reactions induced by ·OH are the main reactions for pollutant degradation in cavitation process.The main methods to enhance the global average hydroxyl radical yield include increasing the hydroxyl radical yield in single bubble event and the promoting cavitation event rate.The choice of optimal upstream inlet pressure and liquid temperature,enhancing the downstream recovery pressure,decreasing the diameters of hole and pipe and increasing the number of holes are helpful to improve the capacity of cavitation for organic pollutant degradation.In experimental research,the novel method of intensifying pollutant degradation by cavitating jets impingement is proposed.A main cavitating jet impingement reactor is designed and the experimental platform for testing organic pollutant degradation process is established.Based on cavitating jet impingement,hydrogen peroxide oxidation,Fenton method,analogous Fenton method and photocatalytic oxidation,degradations of wastewater containing single component Rhodamine B and multi-components antibiotics are conducted.Effects of jet impinging form,nozzle inlet pressure,liquid temperature,initial solution pH and concentrations of additives are analyzed.The synergetic effects of the advanced oxidation processes in organic pollutant degradation are quantitatively illustrated and a wastewater treatment method by combining advanced oxidation processes for industrial application is developed.Experimental results show that the Rhodamine B degradation process conforms to pseudo-first-order kinetics and jet impingement reinforces the degradation.A maximum degradation rate of 71.11%is achieved using individual application of cavitating jets impingement under the optimum conditions.Combination of cavitating-jets impingement and Fenton chemistry can realize the complete degradation of Rhodamine B and the current device proves to have certain advantages of decreasing the hydrogen peroxide usage and higher energy efficiency as compared to other cavitation devices.The wastewater treatment system,which is based on the combinations of advanced oxidation processes,can bring about 79.92%COD reduction of the antibiotics solution under the optimal conditions.The perpendicular double cavitating jet impingement shows the strongest reinforcement for antibiotics degradation.The synergetic effects of different advanced oxidation processes on simultaneous degradation of antibiotics are confirmed.Taking an overall consideration of COD reduction rate and economic,the combination of cavitating jets impingement,UV/Fenton,analogous Fenton and photocatalytic oxidation is proved to be appropriate method for antibiotic wastewater treatment.