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•OH Inactivation of Cyanobacterial Blooms and Degradation of Toxins in Drinking Water Treatment System

Bai, Mindong, Zheng, Qilin, Zheng, Wu, Li, Haiyan, Lin, Shaoyun, Huang, Lingfeng, Zhang, Zhitao
Water research 2019 v.154 pp. 144-152
DNA, Microcystis, benzene, byproducts, carboxylic acids, coagulation, disinfection, drinking water treatment, equipment, filtration, flow cytometry, human health, hydroxyl radicals, ionization, microcystin-LR, mucilages, organic matter, oxygen, sand, scanning electron microscopy, sodium hypochlorite, water quality, water supply, China
Cyanobacterial blooms continue to serve as one of the most serious global issues threatening water supply and human health. During cyanobacterial bloom season, a large •OH-yield equipment was developed and installed after coagulation settling in a 12000 ton/day drinking water treatment system in Xiamen, China. An •OH concentration of 7.76∼57.8 μmol/L was formed by using the oxygen activated species generated by strong ionisation discharge combining with the effect of water jet cavitation. •OH pre-treatment at a dose of 1.0 mg/L inactivated cyanobacterial blooms in the process of conveying bloom water within only 20s, which were then removed by sand filtration. Under SEM observation, dominant Microcystis sp. colonies connected by mucilage were dispersed into individuals that still retained the cell integrity, indicating no release of intracellular organic matter (IOM). According to a flow cytometry analysis, the main cause of •OH inactivation was the breakage of DNA strands. Meanwhile, the •OH-mineralized microcystin-LR was by breaking the C=C conjugated diene bond and crucial opening the persistent benzene ring to carboxylic acid m/z 158.0. During •OH pre-treatment of 1.0 mg/L and NaClO disinfection of 0.5 mg/L, all water quality indexes and disinfection by-product (DBP) contents complied with the Chinese Sanitary Standards for Drinking Water. Therefore, the •OH based on the strong ionisation discharge showed great prospect for large-scale drinking water treatment in the removal of cyanobacterial blooms while retaining cell integrity as well as the degradation of toxins.