Study On The Degradation Efficiency And Oxidation Mechanism Of Brominated Phenol By UV/chlorine

Bromophenol compounds?BPs?in water have attracted extensive attention and research in the field of water treatment because of their harmness.Advanced oxidation processes?AOPs?based on free radicals are effective in removing mircropollutants and have been widely used in the advanced treatment of drinking water and sewage.UV/HOCl advanced oxidation technology as a new water treatment technology,can produce hydroxyl radical?HO·?and a variety of active chlorine radicals?RCS?.Because UV/HOCl has a great ability to remove organic matter by oxidation,it provides a new idea for the effective degradation of BPs in water.This project attempts to construct a UV/HOCl system and use it to degrade BPs of representative micro-polluted organic matter.The research results are as follows:?1?In this paper,by comparing the degradation efficiency of UV/HOCl process and HOCl process for 2-bromophenol,2,4,6-tribromophenol,the effects of different background componets in water on of the degradation efficiency of BPs were sdudied,and by adding radical scavengers further analysis to the degradation efficiency of BPs by different oxidizing componets in the water.Finally,the products formation and degradation pathways of 2-bromophenol and 2,4,6-tribromophenol in UV/HOCl process were investigated to analyze the degradation and transformation mechanism of BPs in UV/HOCl process.The results showed that the degradation efficiency of2-bromophenol,2,4,6-tribromophenol could be significantly promoted by UV-catalyzed HOCl.Compared with the HOCl process,the degradation efficiency of UV/HOCl process in pure water system was increased by 17%and 31%,respectively.In the UV/HOCl system,hypochlorous acid oxidation plays a major role in the degradation of 2-bromophenol,followed by reactive chlorine radical and hydroxyl radical,with contribution rates of 48.9%,31%and 19%,respectively.The degradation of 2-bromophenol by UV alone oxidation is not obvious.For 2,4,6-tribromophenol,hypochlorous acid oxidation alone,HO·and RCS have similar contributions,which all play a major role in degradation.Similarly,UV alone has a lower contribution efficiency to degradation of 2,4,6-tribromophenol.?2?This study investigated the effects of background substances such as chloride ion?Cl^-?,carbonate/bicarbonate(CO₃^2-/HCO₃^-)and natural organic matter?NOM?on the degradation of 2-bromophenol and 2,4,6-tribromophenol in UV/HOCl process.The results showed that UV/HOCl could degrade 2-bromophenol and2,4,6-tribromophenol effectively in the presence of background materials,and the degradation efficiency was improved compared with that of HOCl process.The presence of NOM for 2-bromophenol and 2,4,6-tribromophenol degradation has obvious inhibitory effect,when the NOM dosing increased from 0 to 5 mgC L^-1,the removal rates 2-bromophenol and 2,4,6-tribromophenol decreased from 93.63%and55.6%to 78.41%and 11.79%,respectively.This is mainly becacuse NOM has an inner filter effect for the photolysis and a scavenging effect on radicals.Low concentration CO₃^2-/HCO₃^-to 2-bromophenol and 2,4,6-tribromophenol degradation has inhibitory effect,while high concentration of CO₃^2-/HCO₃^-can promote the degradation of targets.This is mainly because with the increase of CO₃^2-/HCO₃^-dosage,the steady-state concentration of HO·and Cl·decreases to a certain threshold and remains stable,while the increase of the concentration of carbonate radical?CO₃^-·?ultimately promote the degradation of targets.When the concentration of Cl^-increased from 0 to 10 mM,2-bromophenol degradation efficiency increased from 77.8%to88.25%,and 2,4,6-tribromophenol reduced from 60.17%to 54.14%,which is due to the contribution of different chlorine free radicals effect:the contribution Cl₂·^-to the degradation of 2-bromophenol is greater than that of 2,4,6-tribromophenol,and the increase of Cl^-can significantly improve Cl₂·^-steady-state concentration,thus caused the Cl^-on the differences of two target effect.The degradation of 2-bromophenol is the fastest when the pH is 7,and the degradation of 2,4,6-tribromophenol is the fastest when the pH is 5.The change of pH affects the morphology of hypochlorous acid in water.Hypochlorous acid produces more free radicals under acidic conditions.Moreover,due to the different pKa of the two target substances,2-bromophenol reacts more rapidly with free radicals under alkaline conditions,resulting in different experimental results.?3?In this study,the possible structure and degradation path of halogenated organic products were also predicted by HPLC/QTOF-MS.The study found that2-bromophenol produced three intermediates products during the degradation of UV/HOCl process,including chlorobenzene,polychlorinated biphenyl and hydroxy--hexachlorobiphenyl;2,4,6-tribromophenol produced two intermediates products during the degradation of UV/HOCl process,including chlorobenzene and benzoquinone.Through the identification of the product,the degradation path of2-bromophenol and 2,4,6-tribromophenol was speculated.The sduty showed that the HO·and RCS mainly detach the Br^-on the benzene ring structure through the electron transfer reaction,accompanied by-OH addition reaction and halogen substitution reaction.In this study,2-bromophenol and 2,4,6-tribromophenol were used as targets to analyze the degradation efficiency and influencing factors of bromine-containing organics in the UV/HOCl system,explain the oxidation contribution of different active components in the system,and predict the degradation mechanism of bromine-containing organics in the system,in order to provide theoretical basis and data support for the engineering application of UV/HOCl technology.