Production and characterization of iron oxide immobilized bioflocculants in the removal of Microcystis aeruginosa from freshwater ecosystems

Harmful algal blooms (HABs) have significantly influenced water pollution and created negative impacts on biotic and abiotic ecosystems. Microcystis aeruginosa was found to be a major cyanobacterium that causes HABs in freshwater ecosystems. In order to remove HABs, a flocculation mechanism was adopted. As synthetic flocculants exhibit toxicity, microbial-based flocculants were used. Further, in this study, iron oxide (Fe3O4) nanoparticles were immobilized with bioflocculants to enhance the efficacy in removing HABs. Initially, the Fe3O4 immobilized bioflocculants were characterized based on UV– visible spectroscopy, FTIR, DLS, SEM, EDX, HR-TEM, XRD, and VSM analysis. Subsequently, Microcystis aeruginosa was cultivated in optimized conditions and its biomass was calculated. Further, about 96% of the flocculation of Microcystis aeruginosa was observed at optimum pH of 7, temperature of 37 °C, agitated rate of 120 rpm, and complete settling time of 60 min. Moreover, Fe3O4 immobilized bioflocculants could be used up to four times, which could help in reducing the treatment cost. Consequently, it was found that flocculation occurred through a bridging mechanism based on zeta potential analysis. Furthermore, a comparative analysis was performed to compare the efficacy of Fe3O4 immobilized bioflocculant with
commercially available flocculants. It was revealed that Fe3O4 immobilized bioflocculant was more efficient than synthetic flocculants. Based on physicochemical parameters, water treated with Fe3O4 immobilized bioflocculants was found to be within the permissible limit of Indian Standards for drinking water. Hence, this method could be effectively used for drinking purposes. Further, the antimicrobial activity of Fe3O4 immobilized bioflocculants exhibited significant activity against water pathogens. Moreover, molecular docking studies revealed that the active compound Lidocaine of Fe3O4 immobilized bioflocculant showed effective binding at threonine-221 of the target with one hydrogen bond interaction. The results of this study
suggest that Fe3O4 immobilized bioflocculants have potential for removing harmful algal blooms from freshwater ecosystems.