Study On The Efficiency And Mechanism Of Ozone Micro-nano Bubbles In Degrading Typical Odor Substances In Drinking Wate

With the development of economy and society,eutrophication of water bodies is becoming more and more serious,which leads to new pollution problems such as smell in drinking water.In the Hygienic Standard for Drinking Water（GB5749-2022）,the importance of sobriotine（GSM）and 2-methylisobcamphenol（2-MIB）in drinking water has been increased.Both of them have been changed from reference indexes to extended indexes,and their content should not exceed 10 ng·L^-1.Traditional water treatment processes such as activated carbon adsorption and biological removal have been widely used to remove odors,but there are many shortcomings such as difficult recycling and disposal of sludge.In the single ozone oxidation,the utilization rate and absorption rate of the traditional dissolution method of ozone are low.To achieve satisfactory treatment effect,a higher dosage of ozone is needed,which is not only expensive,but also makes the bromate concentration of the treated effluent exceed the standard.As a new technology,micro nano bubble technology has many advantages,such as high gas-liquid mass transfer efficiency,more free radicals and higher zeta potential at the interface.In this thesis,ozone micro-nano bubble system is formed by combining ozone with micro nano bubble technology.The performance of the system is evaluated by comparing with the traditional ozone bubble system.The changes of conventional indexes and the concentration of odors in actual water treated by this system were explored,and the effects of various factors on the odors removal process by ozone micro-nano bubble technology were analyzed.The products of 2-MIB and GSM degraded by the system were compared and analyzed,the oxidative degradation path was speculated,and the deodorization mechanism of the system was explored deeply.The bubble properties of ozone micronano bubble system were tested by high speed camera and laser particle size analyzer.It was found that the particle size was small and the residence time was long.The particle size of the micronano bubbles produced by ozone as the air source is mostly distributed in the range of 15-95μm,and the particle size of the bubbles decreases with the increase of ozone concentration.The mass transfer efficiency of ozone and the concentration of ozone in liquid phase were significantly improved by micro-nano bubble method.In addition,the ozone absorption rate and utilization rate under micro-nano bubbles are higher,up to 95%and 91.25%.The exposure of hydroxyl radical in the ozone micro-nano bubble system can reach 6.31×10^-10 mol·L^-1·s,which accelerates the decomposition of ozone,dissolves more ozone at the same time,improves ozone concentration,and greatly improves the overall oxidation capacity of the system.Using ozone micro-nano-bubble system to treat reservoir water and filter effluent of a water plant were analyzed.The formation of flocs by the aggregation of molecular substances led to the increase of turbidity in both kinds of water bodies.The degradation effect of UV₂₅₄ in the reservoir water was good,the p H was basically unchanged,the concentration of ammonia nitrogen increased,and the dissolved organic carbon（DOC）was partially removed due to the limited mineralization ability of ozone.The removal rate of olfactory substances in two kinds of water is more than 90%,and the effluent concentration is stable.At low ozone dosage,trihalomethane concentration and bromate production meet the sanitary standards for drinking water.In the analysis of influencing factors,ozone concentration and p H value were positively correlated with the removal rate of olfactory substances,while the initial concentration of olfactory substances,the concentration of natural organic substances and the concentration of bicarbonate were negatively correlated with the removal rate of olfactory substances.Due to the different spatial structure,2-MIB is more difficult to remove than GSM.The degradation products of 2-MIB are composed of stereoscopic bridge structure compounds dominated by dextrocamphor and other planar structure substances.The degradation products of GSM mainly include ketones,naphthalene and other alkanes and alcohols.In the process of 2-MIB oxidative degradation,the bridge ring breaks,opens epoxidation,and finally decomposes gradually,in which the elimination of water molecules plays a key role.GSM,on the other hand,generates isomers and other double-ring materials,and then breaks the rings until they are oxidized into small molecular compounds.The toxicity of most degradation products of 2-MIB was reduced,while the toxicity of half of the degradation products of GSM was stronger and the other half was weaker than that of GSM.The oxidation decomposition of 2-MIB and GSM mostly depends on hydroxyl radical and superoxide radical,and the main oxidation factor is superoxide radical.When the air micro nano bubble system degrades odor substances,the main removal effect is physical volatilization,and its contribution ratio to the oxidation of hydroxyl radical is 75:25.