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Kinetics and mechanism of Pseudoanabaena cell inactivation, 2-MIB release and degradation under exposure of ozone, chlorine and permanganate

Li, Lei, Zhu, Cuiwen, Xie, Chuanqi, Shao, Chen, Yu, Shuili, Zhao, Laicai, Gao, Naiyun
Water research 2018 v.147 pp. 422-428
2-methylisoborneol, Pseudanabaena, algae, cell membranes, cell viability, chlorine, kinetics, microcystins, off flavors, oxidants, oxidation, ozone, pollutants, potassium permanganate
The organic pollutants produced by cyanobacteria cells, such as off-flavor compounds (e.g. 2-methylisoborneol, 2-MIB) and hazardous toxins (e.g. microcystins), are commonly detected in water sources. Although studies have shown that oxidation using potassium permanganate (KMnO4), chlorine and ozone helps to remove cyanobacteria cells, the potential effects of these oxidants on cell viability and the release of off-flavor substances have scarcely been explored. This study investigated the impacts of three widely used oxidants on Pseudanabaena sp. (a common species of 2-MIB producing cyanobacteria) inactivation, and on the release and degradation of intracellular 2-MIB. Experiments using KMnO4 showed that both the cell viability and 2-MIB release fit to a two-stage second-order kinetic model with a threshold of KMnO4 exposure (ct). No significant variations in the cell viability and 2-MIB release occurred until the exposure reached ct because KMnO4 was primarily consumed by the dissolved and cell-bound organic matters before it damaged the cell. However, chlorine permeates the cell membrane more easily, causing rapid algae inactivation and the subsequent cell lysis and 2-MIB release. Unlike permanganate and chlorine, which are unable to degrade the released 2-MIB because of their insufficient oxidation potentials, ozone is capable to inactivate the cell and degrade 2-MIB as well. When the initial O3 concentration is above a certain level (1.0 mg ·L⁻¹ in this study), the released 2-MIB can be substantially oxidized. Therefore, the choice of a suitable oxidant and a proper dose is highly important in the control of off-flavor compounds during the treatment of algae-containing raw water.