Effect of moderate pre-oxidation on the removal of Microcystis aeruginosa by KMnO4–Fe(II) process: Significance of the in-situ formed Fe(III)

This study developed a novel KMnO4–Fe(II) process to remove the cells of Microcystis aeruginosa, and the mechanisms involved in have been investigated. At KMnO4 doses of 0–10.0 μM, the KMnO4–Fe(II) process showed 23.4–53.3% higher efficiency than the KMnO4–Fe(III) process did. This was first attributed to the moderate pre-oxidation of M. aeruginosa by KMnO4, achieved by dosing Fe(II) after a period of pre-oxidation, to cease the further release of intracellular organic matter (IOM) and the degradation of dissolved organic matter (DOM). The extensive exposure of M. aeruginosa to KMnO4 in KMnO4–Fe(III) process led to high levels and insufficient molecular weight of DOM, inhibiting the subsequent Fe(III) coagulation. Additionally, Fe(II) contributed to lower levels of the in-situ formed MnO2, the reduction product of KMnO4 which adversely affected algae removal by Fe(III) coagulation. However, the in-situ formed Fe(III), which was derived from the oxidation of Fe(II) by KMnO4, in-situ MnO2, and dissolved oxygen, dominated the remarkably high efficiency of KMnO4–Fe(II) process with respect to the removal of M. aeruginosa. On one hand, in-situ formed Fe(III) had more reactive surface area than pre-formed Fe(III). On the other hand, the continuous introduction of fresh Fe(III) coagulant showed higher efficiency than one-off dosage of coagulant to destabilize M. aeruginosa cells and to increase the flocs size. Moreover, the MnO2 precipitated on algae cell surfaces and contributed to the formation of in-situ formed Fe(III), which may act as bridges to enhance the removal of M. aeruginosa.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (157 K)Download as PowerPoint slideHighlights► KMnO4–Fe(II) process shows much higher algae removal than KMnO4–Fe(III) process. ► Fe(II) ceases the algae inactivation by KMnO4 to avoid extensive cell rupture. ► Continuous formation of in-situ Fe(III) that is more effective than pre-formed one. ► Larger flocs were formed by the continuous Fe(III) provision than one-off dosage.