Simultaneous removal of cyanobacteria and algal organic matter by Mn(VII)/CaSO₃ enhanced coagulation: Performance and...

Frequent outbreaks of algal blooms greatly threatened drinking water safety, garnering widespread attention. Mn/CaSO₃ is emerging in the field of organic matter removal with its efficient oxidizing capacity and wide pH application range. The performance of Mn(VII)/CaSO₃ as a pre-oxidation process enhancing coagulation for algae removal (Microcystis aeruginosa, 2 (±0.5) × 10⁶ cells/mL) was investigated. The results suggested that the Mn(VII)/CaSO₃ process efficiently achieved over 90 % removal of algae cells, notably with a reduced chemical dosage (5.0 μM Mn(VII) and 40.0 μM CaSO₃). Simultaneously, algal organic matters (AOM) and microcystins were effectively controlled due to the oxidative degradation of Mn(VII)/CaSO₃ and the formation of denser flocs owing to the in-situ MnO₂ generation. In addition, it demonstrated that the addition of CaSO₃ broadened the pH range for Mn(VII) application and reduced the Mn residue. Subsequent experiments conducted in this study, such as electron spin resonance, methyl phenyl sulfoxide probe and free radical quenching experiments, demonstrated that Mn(III) may be the key active substance of the Mn(VII)/CaSO₃ system enhancing coagulation for algal removal. Active radicals (SO₄•^- and •OH) in this system also played a relatively minor role. In conclusion, this study highlights the potential of the Mn(VII)/CaSO₃ process as an environmentally friendly adjunct technology for algal removal and AOM control.