Study Of The Degradation Of Bisphenola In Water By High-gravity Advanced Oxidation Processes

Deriving from the phenol and acetone industry chain,Bisphenol A（BPA）is an important chemical intermediate material in the petrochemical industry chain,which is the monomer raw material for the production of polycarbonate and epoxy resin.Nevertheless,BPA is a typical endocrine disrupting chemical with estrogen effect,which harms the growth,development and reproduction of creatures by affecting their normal endocrine system.BPA is widely distributed in the water environment,with stable chemical structure and relatively low content,but long-term exposure to BPA has serious adverse effects on creatures.Hence effective removal of endocrine disrupting chemicals from water is a hotspot of current environmental research.Ozone（O₃）has strong oxidizing ability and O₃-based advanced oxidation is a promising water treatment technology.However,O₃with the shortcomings of low solubility and slow mass transfer rate has limited its application in water treatment.High gravity technology can intensify the mass transfer and mixing performances between and within phases,thus improving the degradation efficiencies of pollutants by enhancing the gas-liquid mass transfer process of O₃.In order to boost O₃mass transfer and BPA degradation efficiency,this study combined O₃-based advanced oxidation processes and high gravity technology for the degradation of BPA in water.The following conclusions have been reached by studies on the degradation of BPA in water with the PRB（Rotating packed bed）-O₃process:（1）The degradation kinetics of BPA was investigated and the effects of different factors on the apparent rate constant k_obswere explored.The experimental results showed that the degradation process of BPA in RPB followed the pseudo-first order reaction.The apparent rate constant increased with the increase of RPB rotational speed,gas phase O₃concentration and solution pH,and decreased with the increase of solution temperature.It was found that the RPB-O₃process degraded most of BPA in a short early stage of the reaction.As the reaction proceeded,the COD and biological acute toxicity of BPA-containing wastewater decreased continuously,and BOD₅and B/C ratio increased first and then decreased.（2）The effects of different factors on the degradation rate of BPA and the total volume mass transfer coefficient（K_Ga）of O₃in the RPB-O₃process were studied.It was found that the degradation rate of BPA increased with the increasing RPB rotational speed,solution pH,gas phase O₃concentration and gas volume flow,and decreased with the increasing BPA concentration and liquid volume flow.K_Ga increased with the increasing RPB rotational speed,solution pH,BPA concentration and gas volume flow,and decreased with the increasing gas phase O₃concentration.Because the residence time of O₃and BPA solution in RPB reactor is short,the generation rate of HO·,initiated by H₂O₂and O₃,is slow.Therefore,the RPB-O₃/H₂O₂coupling process has no significant difference on the degradation of BPA compared with the RPB-O₃process,suggesting that the reaction rate between reactants is an important factor affecting the reaction performance in PRB.Because Fe²⁺is reductive and can be reduced by O₃,it competes with BPA for O₃.The RPB-O₃/Fe²⁺coupling process thus has an inhibitory effect on the degradation of BPA.（3）Response surface methodology（RSM）was used to optimize the BPA degradation process.The interaction of various factors on BPA degradation efficiency was investigated.RSM,artificial neural network（ANN）and multiple linear regression（MLR）models for predicting BPA degradation rate were established and compared.RSM model analyses showed that the order of importance of the factors affecting BPA degradation was solution pH>gas phase O₃concentration>liquid volume flow>RPB rotational speed.There is no significant interaction between RPB rotational speed and other factors.Correlation coefficient（R）,determination coefficient（R²）,mean square error（MSE）and mean absolute error（MAE）were used to evaluate the prediction performances of RSM,ANN and MLR models.It was found that RSM and ANN have better fitting performances on the degradation efficiency of BPA.There is significant deviations in the data of MLR model,suggesting a relatively poor performance.Under the optimal operating conditions of C_O3=20 mg/L,pH=11,L_BPA=10 L/h and Rs=800 rpm,the actual BPA degradation efficiency reached the highest value of 99.52%,and the predicted values by RSM,ANN and MLR models were 99.54%,99.82%and 105.34%respectively.（4）The effect of co-existing chemicals in water on BPA degradation efficiency was investigated.Cl^-and Ca²⁺in water has no significant effect on the degradation of BPA in the RPB-O₃process.HCO₃^-and a certain amount of Mg²⁺can improve the degradation efficiency of BPA in the RPB-O₃process.Due to a competition with BPA,the addition of glucose and fulvic acid reduced the BPA and COD degradation efficiencies significantly.（5）The degradation mechanism of BPA in the PRB-O₃process was revealed via the analyses of the reaction mechanism.The radical quenching experiments proved that O₃and HO·both contribute the degradation of BPA from pH=3-11,and the direct reaction between O₃and BPA is the principal degrading route of BPA.The products and pathway of BPA removal by RPB-O₃process was deduced by UV absorption spectrum and LC-MS analysis.BPA degradation products include 4-hydroxyacetophenone,2,4-di-tert-butylphenol,3,5-di-tert-butylphenol,hydroxy diphenyl ether,etc.Meanwhile,it was found that the addition of H₂O₂and Cl^-does not affect the pathway and products of BPA degradation by the O₃process.