Removal of Microcystis aeruginosa and microcystin-LR by UV/Fenton system: Characteristics and degradation pathways

The increasing severity of cyanobacterial blooms owing to eutrophication in water bodies has caused widespread concern. In this study, the UV/Fenton system was evaluated for the removal efficiency of Microcystis aeruginosa, algal organic matter (AOM), and the intermediate degradation products of microcystin-LR (MC-LR) and their degradation pathways. Studies have shown that under the conditions of 300 μmol·L-1 H2O2, 125 μmol·L-1 FeSO4, 5 min UV irradiation (UV irradiation dose of 14.40 mJ·cm−2), and 10 min pre-oxidation, the removal rates of algae cells were 97.3 %, while the proteins with aromatic structures and soluble biological metabolites in the extracellular organic matter were significantly reduced, with low Fe and AOM residues reported at the end of sedimentation. Liquid chromatography-mass spectrometry analysis showed that HO produced in the UV/Fenton system can attack several reaction sites in the MC-LR molecule, including the aromatic ring and conjugated diene on the side chains of the Adda group, the CC bond of the Mdha group, and the amide bond on the polypeptide ring, and eventually mineralize to CO2, H2O, and inorganic ions. Therefore, the studied UV/Fenton system is an effective method for algae removal and MC-LR degradation, without secondary pollution.