Study On The Formation Mechanism And Quantitative Structure-activity Relationship Of Nitrosamine By-products In Ultrasonic Water Treatment

Ultrasound is a new and environmentally friendly water treatment technology.In recent years,ultrasound has made great progress in removing refractory organic compounds and inhibiting inactivated algae.Moreover,it can be combinated with other water treatment technologies.Previous studies had focused on the efficacy and mechanism of ultrasonic cavitation oxidation for degradation of organic pollutants in water,but neglected the nitrification side reactions induced by nitrogen fixation in ultrasonic cavitation process,as well as the high toxic and carcinogenic nitrosamines by products.This study is the first systematic study on the generation mechanism of nitrosamine by-products and the recognition of molecular characteristics of precursors in the ultrasonic water treatment process.In the process of ultrasonic cavitation oxidation,it was found that the formation rate and maximum molar conversion of NDPhA,NDBA and NDPA were much higher than those of other nitrosamines.It can be attributed to the precursor DPhA,DBA and DPA are all hydrophobic non-volatile substances,including the corresponding nitrosamines generated by them,which also have similar properties and tend to be attached to the gas-liquid interface with high concentration of·NO,and then react with·NO.The relation between the formation rate and frequency of the nine nitrosamines is 600 kHz>400 kHz>200 kHz.The specific relation between the maximum molar conversion rate of NDPhA and the change of ultrasonic frequency is600 kHz>200 kHz>400 kHz.The maximum conversion rate of the other eight nitrosamines with the change of ultrasonic frequency is 600 kHz>400 kHz>200 kHz,which indicates that the generation of nitrosamines is related to the ultrasonic cavitation intensity.The formation rate constant and the maximum molar conversion rate of nine nitrosamines all increase with the increase of sound energy density,which is account for the increase of sound energy density leads to the increase of nitrite?·NO and N₂O₃,etc.?in the system,making the formation rate and the theoretical maximum molar conversion rate increase.All the nine nitrosamines had the maximum molar conversion at pH=7.The formation rate of NDPhA was the fastest at the pH=3,while the other eight nitrosamines were the fastest at the pH=7.Because pH affected the existence form of precursor molecules and the activity of·OH and·NO.The formation rate of nine nitrosamines increases with the increase of the initial concentration of secondary amine,which can attribute to the probability of the contact and collision of·NO and nitrogen-oxygen active substances produced in the ultrasonic cavitation process with secondary amine increases.The presence of Br^-promoted the formation of nitrosamines,while PO₄^3-and NH₄⁺inhibited the formation of nitrosamines,and PO₄^3-had a significant inhibitory effect on the formation of nitrosamines.This is because the presence of inorganic ions affects the amount of nitrogen oxides and·OH required for the formation and degradation of nitrosamines.Based on the experiments conducted in this study,the maximum molar conversion rate and the formation rate of nitrosamines in the ultrasonic process were obtained.The QSAR of the nitrosamines formation rate constant model 1 and the maximum molar conversion rate model 2 were established respectively by using Gaussin,SPSS and other software and using multiple linear regression?MLR?mathematical algorithm.The equation of model 1 is k=0.768Q_N^-+0.308log_kow+1.18x10^-15.The equation of model 2was Y=0.932MV+3.356x10^-16.The models both have good fitting ability,robustness and prediction ability.At the same time,the maximum molar conversion rate and nitrosamine formation rate of the two groups of nitrosamines were obtained through the experiment which shows that the model has good fitting ability.At the same time,the formation rate of nitroso ethylaniline and the theoretical maximum molar conversion rate were obtained through experiments to verify the model,which showed that the model was reliable,could preliminarily predict the formation rate and the maximum molar conversion rate of nitroso ethylaniline,and could analyze the formation mechanism of nitroso ethylaniline.