| Nowadays,dyes have been applied to food,medicine,makeup,printing and dyeing and other industries widely,but the pollution problem of dye wastewater is becoming increasingly serious.As a big dye consuming country in China,the amount of dye wastewater produced is as high as（400～500）×104m3·d-1,and most wastewater has the characteristics of complex composition,high organic matter concentration,high chroma and difficult degradation,etc.these make them belong to one of the industrial wastewater that is difficult to treat at present.Once these dye wastewater is discharged into the water body,it will pose a great threat to the aquatic environment.More seriously,some organic dyes have been proved to cause chromosome variation,thus causing canceration and endangering the safety of animals and human beings.What`s more,the effective removal of organic pollutants from dye wastewater is crucial for maintaining ecosystem balance and ensuring human health.Hydrodynamic cavitation（HC）technology,as a new advanced oxidation technology,has been studied widely because of its advantages of low energy consumption,large treatment capacity,relatively simple follow-up maintenance and repair of equipment,and no secondary pollution in recent years,and has been applied to treating industrial organic wastewater initially.In this paper,the limitation of using only positive pressure cavitation in traditional hydrodynamic cavitation method was broken through,and the degradation of organic dyes was studied by combining positive pressure cavitation with negative pressure cavitation for the first time.This method significantly improves the degradation efficiency of a single cycle of the hydrodynamic cavitation system,and explores the best hydrodynamic cavitation treatment effect by optimizing various equipment parameters and experimental operation parameters of the cavitation system continuously.In this paper,orifice plate was used as hydrodynamic cavitation generator,and cationic dye methylene blue（MB）solution was used to simulate organic dye wastewater.The difference of degradation effect of cavitation system on dye wastewater under different conditions was discussed.The main research results are as follows.（1）In this paper,the cavitation effect of different orifice numbers of positive and negative pressure orifice plates was studied first,and the degradation rate of MB under the optimal combination was compared with that under the hydrodynamic cavitation of positive and negative pressure alone.The results show that the combined cavitation degradation effect of 25-hole orifice plate under negative pressure and3-hole orifice plate under positive pressure（27.62%）is much higher than that of single positive pressure cavitation degradation（16.23%）and single negative pressure cavitation degradation（7.92%）.Obviously,the hydrodynamic cavitation effect produced by negative pressure has a very good auxiliary effect on the improvement of the overall hydrodynamic cavitation intensity.（2）The effects of initial dye concentration,solution temperature and operating inlet pressure on the simultaneous degradation efficiency of negative pressure assisted positive pressure hydrodynamic cavitation were also studied in this paper,and the best treatment conditions of hydrodynamic cavitation system were obtained.The results show that under the operating conditions of 30℃,5.0 bar inlet pressure and the initial concentration of methylene blue（MB）dye of 10 mg/L,the negative pressure assisted positive pressure hydrodynamic cavitation synchronous degradation system has the best degradation effect.（3）Combined with the above optimized conditions,the influence of oxidant such as hydrogen peroxide（H2O2）on the degradation effect of negative pressure assisted positive pressure hydrodynamic cavitation system was further studied.Under the given experimental conditions,for the MB simulated dye wastewater containing50 mg/L H2O2with a concentration of 10 mg/L,the degradation rate of MB in the wastewater by HC can reach 97.52%in a continuous cycle degradation of 150 min.This shows that adding inorganic oxidants such as H2O2can significantly improve the degradation effect of hydrodynamic cavitation.（4）On the basis of optimized conditions,Binding methylene blue belongs to the properties of basic dyes,The degradation efficiency of methylene blue in dye wastewater by hydrodynamic cavitation system under the p H value adjusted by different kinds of inorganic acids was explored,and the effects of different inorganic acid radical ions and different solution p H values on the degradation of methylene blue by hydrodynamic cavitation were studied.The most suitable types of inorganic acids and the best p H conditions were obtained.The results showed that under the acidic condition of adjusting p H=3.0 with H2SO4,the hydrodynamic cavitation system had the best degradation effect,and the degradation rate was 74.08%.（5）Finally,under the optimum conditions,by adding hydroxyl radical inhibitors,the degradation mechanism of hydrodynamic cavitation was explored.The formation of main intermediate products in the process of hydrodynamic cavitation degradation of methylene blue was confirmed by liquid chromatography-mass spectrometry,and the hydrodynamic cavitation degradation process of methylene blue was further clarified.This study provides a very feasible method for energy-saving,efficient and large-scale treatment of organic dye wastewater,and provides wider application of hydrodynamic cavitation technology with reliable theoretical basis and technical support in the future. |
