Study On High Efficiency Degradation Of Atrazine By Hydraulic Cavitation And Oxidant

Atrazine（ATZ）,as a triazine herbicide,is widely used in agricultural weeding.Atrazine,a potential carcinogen,is listed by the European Commission,the Environmental Protection Agency of the United States and the Ministry of Ecology and Environment of China as priority controll pollutants in water bodies.How to effectively remove the residual atrazine in water has become a research hotspot in the field of environmental pollution control.Traditional methods such as physical adsorption,bioremediation and chemical oxidation can not achieve satisfactory results,so it is necessary to develop an economical and effective treatment method with practical application value.Hydraulic cavitation（HC）is considered as a promising oxidation technology due to its advantages of high energy efficiency,economy and simple operation.In the last decade,some understanding of the fundamental variables of hydraulic cavitation has been developed,providing a theoretical basis for its application to free radical induced chemical reactions.For example,the local pressure drop caused by the mechanical rotation of the shrink,vortex diode and other rotary devices will produce cavities,so that the local pressure and kinetic energy in the flowing liquid dramatic changes,resulting in temperature and pressure respectively about5000 K and 1000 atmospheres of extremely high hot spots,resulting in the oxidation of pollutants.However,there are few studies on the degradation of atrazine by HC oxidation.Therefore,the degradation pathway and oxidation mechanism of atrazine under hydraulic cavitation were systematically studied in this paper.The main research contents and conclusions are as follows:1.To explore the cavitation effect of the hydraulic cavitation device.Firstly,the pressure,velocity and bubble cloud of Venturi cavitation device are calculated by CFD simulation,and the flow field of cavitation is determined.The main species of reactive oxygen species produced by hydraulic cavitation device are hydroxyl radical（·OH）,a small amount of superoxide radical（·O₂^-）and singlet oxygen（¹O₂）by probe experiment.The concentration of·OH was determined under different conditions.It was found that p H=3.03（0.3μM of·OH）、0.15 MPa（0.1μM of·OH）、40℃（1.6μM of·OH）and dissolved oxygen content 7.2 mg·L^-1（1.0μM of·OH）in HC system were more favorable for the formation of·OH In addition,with the increase of dissolved oxygen content,the presence of·O2^-and ¹O₂ in the system continuously indicates that oxygen partially dissolved in water can be converted into reactive oxygen species to realize the degradation of pollutants.The above results indicate that the cavitation of Venturi device is to produce reactive oxygen species,and it is also found that activated molecular oxygen can be transformed into reactive oxygen species such as·OH,·O₂^-and ¹O₂.2.To solve the problem of low HC degradation efficiency,HC activated persulfate（PDS）was used to improve its Atrazine（ATZ）oxidation efficiency.The results showed that the degradation of ATZ by 0.37 m M PDS at 0.15 MPa and 30℃was 94.1%after 180 min,and the mineralization rate reached 44.9%.The main degradation pathway in this case was dealkylation chain.It was found that when the ratio of sulfate radical（·SO₄^-）to hydroxyl radical（·OH）was close,the best removal effect was obtained.It was also found that ATZ had different mineralization effects and degradation paths with different free radical contribution ratios.If the dosage of PDS is increased,·SO₄^-is the dominant reactive oxygen species,which can accelerate the degradation of ATZ.After 60 min,the removal rate and mineralization rate are94%and 8.8%（3.7 m M PDS）,respectively.The main degradation path is the oxidation of alkyl chain into olefin chain.When the p H value of the regulatory system is 3.5,the degradation and mineralization of ATZ can be further accelerated by making·OH the dominant reactive oxygen species.After 30 min,the removal rate is 97.5%and the mineralization rate reaches 77.4%,and the main product is the de-chlorination substituted product.Therefore,the dominant active species in the system can be regulated by changing the operating conditions to change the main degradation pathway and cavitation effect of ATZ.At the same time,ECOSAR software was used to predict the toxicity of ATZ degradation intermediates to fish,daphnia and green algae,and it was found that the acute toxicity of ATZ intermediates to fish and Daphnia was lower than ATZ itself.3.The traditional combined processes of HC and H₂O₂ have better degradation performance only under acidic conditions.In order to expand the p H range of the system,the degradation efficiency of ATZ in the whole system(HC at 0.15 MPa,30℃,0.3 g·L^-1 H₂O₂,p H=6.2)was improved by adding a small amount of ascorbic acid（0.6 m M AA）.ATZ could be completely removed in about 240 min.The main reason is that ascorbic acid can activate the decomposition of H₂O₂ by HC to produce more hydroxyl radicals（·OH）,so as to achieve the efficient degradation of ATZ.The toxicity of ATZ itself and its degradation intermediates to fish,daphnia and green algae in HC-H₂O₂ and HC-AA-H₂O₂ systems was predicted by ECOSAR software.It was found that the effects of ATZ intermediates on acute toxicity to green algae and chronic toxicity to three organisms were not significant.But the acute toxicity to fish and daphnia was significantly lower than ATZ itself.