| The increasing severity of cyanobacterial blooms due to eutrophication in water bodies has caused widespread concern.Microcystis aeruginosa can grow uncontrollably in eutrophic water bodies,resulting in significant release of algal organic matter（AOM）and microcystins,posing a serious threat to the water quality safety of drinking water.It is difficult to remove both algae cells and algal toxins by conventional water treatment process due to the negative surface charge of algae cells,electrostatic repulsion and spatial potential resistance effect.Therefore,it is important to find a high removal rate,low cell damage and green and pollution-free algae removal technology.In this thesis,we investigated the effect of UV/Fenton oxidation system on the removal of Microcystis aeruginosa,algal organic matter and microcystis,optimized the algae removal conditions using response surface optimization method,and explored the coagulation mechanism of algae cells and the fluorescence change characteristics of algal organic matter;finally,we analyzed the main degradation products of Microcystin-LR（MC-LR）and its possible degradation pathways.The main findings of the study are as follows:（1）The UV/Fenton system can effectively remove Microcystis aeruginosa cells and algal organic matter,while forming in situ Fe（III）to enhance the coagulation treatment effect.Through response surface optimization experiments,the optimal conditions for algae removal were:H2O2 dosing of 300μmol·L-1,Fe SO4 dosing of 125μmol·L-1,UV irradiation time of 5 min,and pre-oxidation time of 10 min.Under the optimal algae removal conditions,the algal cell removal rate was 97.33%,and the residual Fe content was lower than the safety limit in surface water;the majority of algal cells remained intact,and only some algal cells were slightly broken,with a breakage ratio of 20.90%;the removal rates of soluble biological metabolites and protein-like substances were88.89%and 88.69%,respectively.This may be due to the fact that during coagulation and precipitation,HO·preferentially coagulates high molecular weight and high aromaticity compounds,and its strong oxidizing property breaks the peptide chain and destroys the function and structure of the protein,thus causing a significant reduction of protein-like substances.And the removal rate of fulvic acid substances was 51.92%.Humic acid-like substances increased by 22.03%,which was presumed to be mainly due to the oxidation or slight breakage of algal organic matter by HO·which caused the release of intracellular organic matter and produced humic acid-like substances;the formation of Fe（III）and Fe（II）flocculating substances effectively promoted algal cell aggregation and sedimentation,and the absolute value of zeta potential was significantly reduced to-3.68 m V,indicating that this system had the best coagulation conditions and the best algal cell aggregation effect was observed.（2）The UV/Fenton system was effective in degrading MC-LR.in the experiment of MC-LR formulated with Milli-Q water,the removal rate of MC-LR under the optimal algae removal conditions was 90.65%;when the initial concentration of MC-LR was increased from 5μg·L-1 to 20μg·L-1,the removal rate of MC-LR decreased from 90.65%to 70.17%,which may be due to the original When the H2O2 dosage was increased from 150μmol·L-1 to 750μmol·L-1,the MC-LR removal rate increased from 84.27%to 92.22%,and all of them were lower than the safety limit of drinking water(1μg·L-1);when the UV irradiation time was increased from 3 min When the UV irradiation time was increased from 3 min to 20 min,the removal rate of MC-LR increased from80.96%to 93.20%,and all of them were lower than the safety limit value of drinking water(1μg·L-1).In the actual algae-containing water experiments,the extracellular MC-LR decreased from 1.85μg·L-1 to 0.40μg·L-1 under the optimal algae removal conditions,with a removal rate of 78.36%,presumably mainly because the UV/Fenton system in practice,algal organic matter（such as humic acid,soluble biological metabolites and proteins,etc.）in the algal solution competed with MC-LR for HO·,thus reduced the removal rate of MC-LR;intracellular MC-LR decreased from 4.12μg·L-1 to 3.60μg·L-1,with little change in intracellular MC-LR before and after treatment,indicating that it did not cause a large amount of intracellular MC-LR release.（3）The degradation pathway of MC-LR released from Microcystis aeruginosa was investigated by LC-MS after oxidation by UV/Fenton system.The five most representative MC-LR intermediate degradation products were detected as m/z 1029.6,1045.6,795.4,233.3 and 131.2,respectively.The degradation pathways inferred from the qualitative analysis of the mass spectra were reported as follows:·OH attacks the conjugated diene double bond on the Adda side chain in the MC-LR molecular structure and undergoes a dihydroxylation addition reaction to produce the three isomeric macromolecules product m/z 1029.6;the aromatic ring on the Adda side chain in product m/z1029.6 undergoes an electrophilic substitution reaction with·OH to produce product m/z 1045.6;the C=C double bond on the Adda side chain in product m/z1045.6 was broken to produce product m/z 795.4 and product m/z 233.3;the amide bond（-CO-NH）on the polypeptide ring of Arg group in product m/z 795.4was broken to produce product m/z 131.2;finally,the intermediate degradation products were completely mineralized to CO2,H2O and inorganic salt ions. |
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