Pre-oxidation with KMnO4 changes extra-cellular organic matter's secretion characteristics to improve algal removal by coagulation with a low dosage of polyaluminium chloride

Microcystis aeruginosa was used to study the effect of KMnO4 pre-oxidation on algal removal through coagulation with polyaluminium chloride (PAC). KMnO4 pre-oxidation improved the coagulation efficiency of algal at a low dosage of PAC. The optimal KMnO4 feeding period was in the stationary growth phase of Microcystis aeruginosa. KMnO4 traumatized the algal cells and stimulated cellular release of organic matter, contributing to the pool of extra-cellular organic matter (EOM). KMnO4 also decomposed EOM, especially small molecular weight EOM. Lower concentrations of KMnO4, such as 2 mg/L, induced algae cells to produce moderate amounts of new EOM with molecular weights of 11, 280, and 1500 kDa. These relatively large molecules combined easily with PAC, promoting coagulation and removal of algae. High concentrations of KMnO4 lysed algae cells and produced much high-molecular-weight EOM that did not enhance flocculation by PAC at lower dosages.