Effective removal of Microcystis aeruginosa and microcystins by integrated pre-oxidation and coagulation: an environmental and economical way

The frequent occurrence of cyanobacteria blooms has gained worldwide concern. The conventional pre-oxidation methods are not only less effective in removing Microcystis aeruginosa cells, but also tend to trigger secondary pollution with an inevitable release of intracellular organic matter. In this study, Fe2+/persulfate process was applied to generate sulfate radicals and simultaneously form in situ Fe (III) for integrated oxidation-coagulation, leading to a notable enhancement in M. aeruginosa removal without cell breakage and better control of microcystins. Results showed that the Fe2+/persulfate mass ratio of 1:1 and the FeSO4 dosage of 0.1 mmol/L were efficient in M. aeruginosa removal. With the optimal FeSO4 dosage, up to 90.1% of M. aeruginosa were removed intact with the cell zeta potential of - 0.814. After settling down of M. aeruginosa within 30 min, the chlorophyll-a removal efficiency reached 98.9% and microcystins decreased remarkably. Furthermore, the degradation of algal organic matters was significantly enhanced with a relatively lower residual Fe. Protein-like substances and dissolved microbial metabolites were preferentially oxidized. The cell lysis only occurred to a small number of M. aeruginosa during the Fe2+/persulfate process, preventing from the environmental risk posed. This work demonstrates that an appropriate Fe2+/persulfate ratio and FeSO4 addition is a feasible and promising method for removing M. aeruginosa in an environmental-friendly and cost-effective way.