A innovative stepwise strategy using magnetic Fe3O4-co-graft tannin/polyethyleneimine composites in a coupled process of sulfate radical-advanced oxidation processes to control harmful algal blooms

Abstract

A novel co-graft tannin and polyethyleneimine co-coating magnetic composite (TP@Fe3O4) was prepared in the study. On this premise, an unique stepwise efficient strategy based on magnetic flocculation and Sulfate radical (SO4•-)-advanced oxidation processes (S-AOPs) for eliminating Microcystis aeruginosa (M. aeruginosa) and algal organic matters (AOMs) was presented. Due to the high positive charge of TP@Fe3O4, a > 99 % high algae removal rate was obtained at a modest TP@Fe3O4 dosage of 100 mg/L at pH = 8.0 with a short separation time of 5 min. Further, peroxymonosulfate (PMS) treatment was employed as a pre-oxidation method to lower cell stability and promote M. aeruginosa removal by subsequent TP@Fe3O4 flocculation. The PMS/TP@Fe3O4 system successfully cuts the optimum dose of TP@Fe3O4 in half (50 mg/L) without causing obvious cell damage. Following algal fast magnetic separation, ultraviolet (UV) was introduced to activate PMS to totally degrade AOM and microcystin. Response surface methodology (RSM) demonstrated that UV/PMS oxidation removed > 80 % of DOC and > 94 % of microcystin under optimal conditions. SO4•- was the main radical species that aided in the elimination of AOM. This is the first study to use magnetic flocculation in conjunction with AOPs to mitigate harmful algal blooms, which can enable the non-destructive eradication of M. aeruginosa while also efficiently degrading AOMs.