Removal of cyanobacteria and control of algal organic matter by simultaneous oxidation and coagulation - comparing the H2O2/Fe(II) and H2O2/Fe(III) processes

Abstract

Cyanobacterial blooms in drinking water are worldwide concern. It is known that pre-oxidation enhanced coagulation can be more efficient at removing algae than traditional coagulation. However, its application is hindered by high oxidant/coagulant consumption and the resultant potential health risk, in the form of algal organic matter (AOM) released during oxidation. To remove the cyanobacteria and meanwhile ensure cell integrity, H₂O₂/Fe(II) and H₂O₂/Fe(III), which have been widely used to degrade organic pollutants in waters, are proposed in this study. The removal efficiency of Microcystis aeruginosa (M. aeruginosa) under various oxidant/coagulant dosages, AOM release and cell integrity, as well as floc formation and morphology were investigated with these simultaneous oxidation/coagulation processes. The results show that the removal efficiency was higher than 95% with H₂O₂/Fe(II) and H₂O₂/Fe(III) under 100 μmol/L H₂O₂ and Fe. In addition, neither method was found to damage the algal cells in 50-200 μmol/L H₂O₂ dosing concentrations. It was also found that AOM, including microcystins (MCs), was well controlled owing to the oxidation of H₂O₂ or hydroxyl radicals, and in-situ Fe(III) settled down the cells in the processes. Compared with H₂O₂/Fe(II), H₂O₂/Fe(III) could remove algae efficiently and control AOM release with lower H₂O₂ (50 μmol/L) and Fe(III) (80 μmol/L) dosages, which suggests that a low chemical consumption is suitable for this simultaneous oxidation/coagulation processes. This is a promising technology for the removal of algae from drinking water in a clean, economical way.

Keywords: Algal organic matters; H(2)O(2)/Fe(II); H(2)O(2)/Fe(III); Microcystis aeruginosa.