Simultaneous removal of algae, microcystins and disinfection byproduct precursors by peroxymonosulfate (PMS)-enhanced Fe(III) coagulation

Abstract

Algae blooms can clog filtration tank, release toxic cyanotoxin and produce undesirable disinfection byproducts (DBPs) in post-chlorination, which brings challenges to conventional water treatment processes. In this study, peroxymonosulfate (PMS) was tested for its ability to improve Fe(III) coagulation of Microcystis aeruginosa in water treatment. Compared with conventional Fe(III) coagulation, the presence of PMS resulted in the formation of larger floc and thus better algae and turbidity removal. The removal of algae by PMS-enhanced Fe(III) coagulation (PMS-Fe(III)) process reached 97.5% at 1 mM PMS, which was 1.5 times higher than that by Fe(III) coagulation alone. The oxidization of surface-adsorbed extracellular organic matter destabilized the algal cells and enhanced their coagulation without greatly damaging the cells’ integrity. Simultaneously, about 80% of Microcystin-LR, a cyanotoxin, was degraded in the enhanced process. Moreover, the formation of DBPs and their associated toxicity during the subsequent chlorination were decreased by 49.2% and 13.6%, respectively. The production of trihalomethanes, haloacetic acids and haloacetronitriles was particularly abated. SO4•- and HO•, which were formed from PMS activation through redox cycling of Fe mediated by the existing natural organic matter, were mainly responsible for algae removal. The results indicate that supplementing Fe(III) coagulation with PMS is a promising option for treating water during algal blooms.