Study On The Generation Mechanism Of DBPs In The Process Of UV-AOP Oxidation Of Algae Organic Matte

Algal organic matter（AOM）is an important organic matter in drinking water source such as lake and reservoir,which brings many difficulties and challenges.Conventional water treatment process is difficult to remove AOM,and its high organic nitrogen content is prone to produce more toxic nitrogen containing disinfection byproducts（N-DBPs）,which poses a threat to human health and drinking water safety.When the water contains halogen ions（Cl^-,Br^-）,the halogenated disinfection byproducts（DBPs）can be produced in the ultraviolet advanced oxidation process.In this study,the oxidative degradation efficiency of AOM and DBPs was studied by UV/chlorine advanced oxidation process（UV/NaClO）and UV/persulfate advanced oxidation process（UV/PDS）.Explore the influence of factors including oxidizer concentration,UV dose,initial p H value,Br^-concentration,Cl^-concentration on DBPs formation rule and the removal effect of precursors,and characterize the characteristics of AOM.The main research contents and test results are as follows:（1）Both UV/NaClO system and UV/PDS system have certain mineralization effect on AOM.When the light intensity is 4000μw/cm²,the oxidant concentration is 20 mg/L,the Br^-concentration is 300μg/L,and the Cl^-concentration is 200 mg/L,the DOC removal rates are21.96%and 31.52%,respectively.The UV₂₅₄removal rates were 36.26%and 48.48%,respectively.Under acidic environment（p H3.00,5.00）,the mineralization effect of AOM is better.With the increase of Cl^-concentration,the removal effect of DOC and UV₂₅₄firstly decreases and then increases.When Cl^-concentration is 500 mg/L,the removal effect of DOC and UV₂₅₄can reach 33.37%and 55.56%.（2）After UV/NaClO oxidation of AOM,DBPs are mainly formed by TCM,DBCM,BCAA and DCAA.Increasing the dosage of NaClO,the concentration of Br^-and the concentration of Cl^-will accelerate the generation of DBPs in the oxidation process of UV/NaClO,and increase the types of DBPs.The weak ultraviolet light can promote the generation of chlorinated DBPs,while the strong ultraviolet light can degrade the DBPs to some extent.In acidic environment,the generation of Br-DBPs is more,in alkaline environment,the generation ratio of THMs at p H 5.00is reduced by 33.08%,HAAs ratio at p H 3.00 reduced by 57.21%.（3）Compared with UV/NaClO system,the total amount of DBPs generated during the oxidation of AOM by UV/PDS is lower,and the types of DBPs produced are different,mainly composed of TCM,DBCM and TCAA.The amount of TCAA produced does not change with the concentration of PDS,Br^-and Cl^-.The increase of PDS dosage,light intensity and Cl^-concentration can inhibit the generation of halogenated DBPs in UV/PDS oxidation system.When the concentration of PDS is 30 mg/L,the concentration of THMs is reduced by 62.49%compared with that of UV alone.When the light intensity is 12000μw/cm².Compared with PDS alone,the concentration of THMs decreased by 65.87%,and Br-DBPs was easily formed under acidic conditions.With the increase of Br^-concentration,the yield of Br-THMs increases.（4）By investigating the effects of NaClO dosage,light intensity,p H value,concentration of Cl^-and Br^-on the degradation of DBPs precursors by UV/NaClO,it was found that increasing NaClO dosage and light intensity would lead to the increase of DBPs FP,while N-DBPs increased with the increase of light intensity.BCAN and DBAN increase 48.88%and 31.57%,respectively,when the light intensity is 12000μw/cm².In acidic environment（p H3.00,5.00）,the removal of THMs,HAAs and other precursors has a good effect,while in alkaline environment,the removal of HANs precursors is more favorable.Br^-has an obvious effect on DBPs FP.With the increase of Br^-concentration,Cl-DBPs transforms to Br-DBPs,and the content of Br-DBPs increases.Cl^-has a certain effect on THMs FP and HAAs FP,but has no obvious effect on HANs FP.The order of influencing factors on the removal rate of THMs and HAAs precursor was PDS dosage>light intensity>p H>Cl^-concentration>Br^-concentration.The order of influence on the removal rate of HANs precursor was light intensity>Br^-concentration>PDS dosage>Cl^-concentration>p H.（5）The effects of PDS dosage,light intensity,pH,Cl^-and Br^-concentration on the removal of DBPs precursors by UV/PDS were investigated.It was found that PDS alone had oxidation capacity and could remove part of DBPs precursors,and the removal rate was increased after UV was added.In acidic environment,the removal rate of HAAs and THMs precursors could reach67.45%and 65.60%.The removal of DBPs precursors was accelerated by increasing the concentration of Cl^-.The order of influencing factors on the removal rate of THMs and HAAs precursor was PDS dosage>light intensity>p H>Cl^-concentration>Br^-concentration.The order of influence on the removal rate of HANs precursor was light intensity>Br^-concentration>PDS dosage>Cl^-concentration>p H.（6）On the whole,UV/PDS system had better removal effect on algal DBPs precursors than UV/NaClO system.Under the same experimental conditions,the removal rates of THMs precursors,HAAs precursors and HANs precursors were 58.65%,47.81%and 60.62%respectively.The removal rates of THMs precursor,HANs precursor and HANs precursor by UV/PDS system were 76.62%,57.30%and 77.93%.（7）Before and after UV/NaClO and UV/PDS reactions,the group types and absorbance of AOM did not change basically,and the aromatic structure of AOM was less;For UV/NaClO system,the contents of humic acid and fulvic acid increased first and then decreased,while the intensity of fluorescence groups in UV/PDS system decreased.With the increase of reaction time,the removal effect of TOC was enhanced.The content of protein and polysaccharide in UV/NaClO system increased first and then decreased,and the content of protein and polysaccharide in AOM was decreased by UV/PDS oxidation.