Novel disinfection method for toxic cyanobacteria (Oscillatoria tenuis) and simultaneous removal of cyanotoxins aided by recyclable magnetic nanoparticles

Abstract

An optimized disinfection method with metal ions to address cyanobacteria contamination in freshwater is presented, based on recyclable magnetic nanoparticles. In this study, the disinfection ability of individual metal ions (Ag+ and Cu2+) and combined (Ag+ + Cu2+) were evaluated with a target cyanobacteria, Oscillatoria tenuis, under various environmental conditions. The usage of combined Ag+ and Cu2+ reduces the time and concentration needed to achieve the same disinfection effectiveness compared to individual metal ions. However, the addition of Cu2+ and Ag+ stimulated production of cyanotoxin during disinfection, with an increase of 24.8% for anatoxin-a. To reduce the potential health risk, we evaluated the recovery and reuse of metal ions, and removal of cyanotoxins after disinfection, using magnetic nanoparticles with permanently confined micelle arrays (Mag-PCMA) under various environmental conditions. Recovery efficiency of Ag+, the most valuable ion, was excellent (99.8%), although it decreased to 74.5% with increasing Cl- concentration (0–10 mg/L). The regeneration and reuse of Mag-PCMA was studied for 5 cycles. Removal efficiency of Cu2+, anatoxin-a and cylindrospermopsin were minimally changed during the 5 sorption-desorption cycles, and that of Ag+ remained above 93% by the end of 5th cycle, indicating that this disinfection method may be sustainable for practical use with low energy requirements and minimized environmental impacts.