Study On The Degradation Characteristics Of Alizarin Yellow R And Orange Ⅳ By UV-catalyzed Persulfate In The Presence Of Bromide Ions

The dye wastewater discharged in the textile industry poses a potential threat to the ecological environment and human health,because of its high organic matter content,deep pigment and difficult degradation.Among these dye wastewaters,azo dye wastewater pollution is particularly prominent.Azo dyes wastewater discharging into the aquatic environment will reduce the transparency of water bodies and affect the growth and reproduction of aquatic organisms.Therefore,this paper focus on the characteristics and mechanism of degradation of azo dyes by UV/PDS advanced oxidation system in the presence of bromine ions,and explores the effects of ultraviolet intensity,bromide ion concentration,p H value,initial dye concentration,inorganic anions（HCO₃^-,NO₃^-）and natural organic matter（NOM）on the degradation kinetics of the two azo dyes,meanwhile the mechanism of two azo dyes degradation by UV/PDS/Br^-advanced oxidation system was elucidated.Based on the response surface method,the Box-Behnken model was used to optimize the optimal reaction conditions for dye degradation,which provided a theoretical basis for deeply studying the degradation mechanism of azo dyes and the influence of different influencing factors on dyes in advanced oxidation systems.The main conclusions are as follows:（1）For the UV/PDS advanced oxidation system in the presence of bromide ions,when the concentration of bromide ions was lower than 0.01m M,the oxidative degradation of alizarin yellow R was inhibited,and when the concentration of bromide ions was from 0.5 to 2m M,the UV/PDS/Br^-advanced oxidation system had a significant promoting effect on the degradation of alizarin yellow R.The removal rate of alizarin yellow R increased with the increase of light intensity.When the p H value increased from 2.9 to 9.7,the removal rate of alizarin yellow R showed a trend of firstly increasing and then decreasing.The higher the initial concentration of alizarin yellow R,the more unfavorable it was to the degradation of dye.Inorganic anions and NOM would inhibit the degradation of alizarin yellow R,and the higher the concentration,the stronger the inhibition effect.According to the results of the univariate influence experiment of alizarin yellow R,the Box-Behnken model of the response surface methodology was used to optimize the reaction conditions of ultraviolet intensity,Br^-concentration and p H,and a secondary polynomial regression model was established,the results of ANOVA showed that the F value of the model was222.37 and the p-value was less than 0.0001,indicating that the model is suitable for analyzing and predicting the degradation process of alizarin yellow R.In the presence of bromide ions,when the p H was 5.60,the concentration of bromide ions was1.77m M,and the light intensity was 13.87u W/cm2,the removal effect of alizarin yellow R in UV/PDS was the best,and the polynomial model predicted that the removal rate of alizarin yellow R was 81.34%,and the experimental average removal of Alizarin yellow R was 79.95%,the error value between the model prediction and experimental value was only 1.71%,suggested that the model could well predict the removal of alizarin yellow R.（2）In the UV/PDS advanced oxidation system in the presence of bromide ions,the oxidative degradation of orange yellow IV was inhibited when the concentration of bromide ions was lower than 0.01m M,but when the concentration of bromide ions was from 0.1 to 1m M,the UV/PDS/Br^-advanced oxidation system had a significant promoting effect on orange-yellow IV.The removal rate of orange yellow IV increased with the increase of light intensity.The higher the p H,the lower the removal rate of orange yellow IV was.The greater the initial concentration of orange-yellow IV,the more unfavorable it is to the degradation of the dye;Both inorganic anions and NOM inhibit the oxidative degradation of orange-yellow IV,and the higher the concentration,the stronger the inhibition effect was.According to the results of the Orange-Yellow IV univariate influence experiment,the Box-Behnken model in the response surface method was used to optimize the Br^-concentration,p H value and reaction time,a second-order polynomial regression model was established,the ANOVA results showed that the F value of the model was 73.98 and the p-value was less than 0.0001,indicating that the model is suitable for analyzing and predicting the degradation process of Orange-Yellow IV.In the presence of bromine ions,when the concentration of bromine ions was 0.77m M,p H was 3.86,and the reaction time was 89.72min,the removal effect of orange yellow IV in UV/PDS was the best,and the polynomial model predicted that the removal rate of orange yellow IV.was 78.5%,and the experimental removal average of orange yellow IV was 77.16%,and the error was only 1.71%,indicating that the model could better predict the removal of orange yellow IV.（3）Through economic benefit evaluation,the effects of the initial concentration,bromide ion,bicarbonate and p H value of alizarin R and orange IV dyes on the energy consumption of dyes degradation by oxidation system were compared.For Alizarin Yellow R,when the initial concentration of dye increased,the EE/O of system gradually increased;When the concentration of bromide ion is 0.01 m M,the EE/O value of the system is 270.819 k Whm^-3,which is higher than that of the system without bromide ions,and when the concentration of bromide ions is 1 m M,the EE/O value of the system is significantly decreased.The EE/O value of the system increases significantly when bicarbonate is present.When the p H value increased from 2.9 to 9.7,the EE/O of the system decreased firstly and then increased.For orange-yellow IV,the higher the initial concentration of orange-yellow IV,the higher the EE/O of the system was;When the concentration of bromide ions is 0.01 m M,the EE/O of the system is higher than that of the system without bromide ions,and when the concentration of bromide ions is 1 m M,the EE/O value of the system was significantly decreased.When bicarbonate is present,the EE/O value of the system increased significantly.The EE/O value of the system increased with the p H increased from 3.6 to 8.2.