Kinetics of cell inactivation, toxin release, and degradation during permanganation of Microcystis aeruginosa

Potassium permanganate (KMnO₄) preoxidation is capable of enhancing cyanobacteria cell removal. However, the impacts of KMnO₄ on cell viability and potential toxin release have not been comprehensively characterized. In this study, the impacts of KMnO₄ on Microcystis aeruginosa inactivation and on the release and degradation of intracellular microcystin-LR (MC-LR) and other featured organic matter were investigated. KMnO₄ oxidation of M. aeruginosa exhibited some kinetic patterns that were different from standard chemical reactions. Results indicated that cell viability loss and MC-LR release both followed two-segment second-order kinetics with turning points of KMnO₄ exposure (ct) at ct_y and ct_r, respectively. KMnO₄ primarily reacted with dissolved and cell-bound extracellular organic matter (mucilage) and resulted in a minor loss of cell viability and MC-LR release before the ct value reached ct _y. Thereafter, KMnO₄ approached the inner layer of the cell wall and resulted in a rapid decrease of cell viability. Further increase of ct to ct_r led to cell lysis and massive release of intracellular MC-LR. The MC-LR release rate was generally much slower than its degradation rate during permanganation. However, MC-LR continued to be released even after total depletion of KMnO₄, which led to a great increase in MC-LR concentration in the treated water.