Effect Of Chloride On The Degradation Performance And Products Of Bezafibrate And Carbamazepine In UV/persulfate Process

In recent years,sulfate radical-based advanced oxidation process of(SR-AOPs)has been researched widely.It has been shown that SR-AOPs can effectively degrade pharmaceuticals and personal care products(PPCPs).However,chloride ions(Cl-)in natural waters can affect the degradation of SR-AOPs,and may even produce chlorinated by-products.Therefore,studying effect of Cl-on the degradation of PPCPs in SR-AOPs is significant to evaluate the potential risks.In this study,benzaflbrate(BZF)and carbamazepine(CBZ)were selected as the target compounds.Based on the kinetic model,the effect of Cl-on the degradation efficiency and products of the two targets in UV/persulfate process were investigated.The results showed that in the UV/PDS process,low concentration of Cl-(<1.0 mM)converted SO4·-into OH· and Cl-,which have higher reactivity with BZF,thus promoted the degradation of BZF.While excessive Cl-(>1.0 mM)converted OH· and Cl-into Cl2·-,which has lower reactivity with BZF and thus inhibited the degradation of BZF.For CBZ,however,a promotive effect was still exliibited after excessive Cl-because of its high reactivity with Cl2·-.Cl2·-predomnated in acidic conditions and OH· predominated in alkaline conditions,which led to the promotion of BZF before pH<7 and the inhibition of BZF after PH>7.But CBZ was observed a higher degradation rate in acidic conditions.In addition,the fitting results of benzoic acid(BA)showed that the changing trends of reactive radical contributions were consistent with that of steady-state concentrations.OH' had been proved to play a significant role in the degradation process.In the UV/PMS process,the change trends of reactive radical concentrations were consistent with that in the UV/PDS process.Non-UV experiments showed that high concentration of HOCI produced at 1 00 mM Cl-can accelerate the degradation of targets.Therefore,BZF degradation rate increased first and then decreased silghtly while CBZ increased continuously slightly when Cl-concentration increased from 0.01 mM to 10 mM.when Cl-concentration was up to 100 mM,both of BZF and CBZ degradation rates increased significantly.The concentrations of SO4·-and OH· increased slowly as pH increasing from 3 to 9,and increased rapidly after pH>9.The concentration of Cl· and Cl2·-decreased with the increase of pH.Acidic condition was favor to produce HOCl,and accelerated the degradation of BZF and CBZ.Therefore,the degradation rates of targets decreased with the decrease of pH,while the degradation rates increased when pH was 3.Few chlorinated products were detected in the UV/PDS/Cl-,indicating that oxidation was the main reaction.In the UV/PMS/Cl-,same chlorinated products were detected when Cl-concentration was excessive,indicating that chlorine substitution reaction happened due to a large number of HOCI produced.