Investigating flocculation mechanisms and ecological safety of cationic guar gum for rapid harvesting of microalgal cells

The synthesized CGG exhibits a green profile, is non-toxic, and demonstrates excellent biocompatibility, which enabling efficient in-situ harvesting of microalgae. [Display omitted] •An environmentally friendly bioflocculant (CGG) was successfully prepared.•CGG was deemed to possess the capability for in-situ microalgae harvesting.•The flocculation mechanism of CGG was predominantly governed by multiple forces.•The flocculation capacity of CGG achieved an impressive 23.5 g/g.•The ecological safety of CGG was evaluated from biological multidimensional. Addressing the drawbacks of traditional flocculants on microalgae biomass harvesting is crucial for large-scale industrial applications of microalgae production. In this study, cationic bioflocculant was successfully prepared by introducing cationic groups into the side chain of guar gum, achieving in-situ algae flocculation efficiency of 83.5 % with the dosage of 18.0 mg/L under pH = 10.0. Through a harmonious integration of predictive modelling and practical experimentation, a superior cell flocculation capacity of 23.5 g/g was achieved. In addition, the environmental safety and biocompatibility of cationic guar gum was assessed, using the typical suspension quantitative bacteriostatic method and the fluorescent double-staining technique. The results showed that the inhibition efficiency of Staphylococcus aureus in the system containing 60.0 mg/L cationic guar gum was only 12.0 % and there was no inhibition against Escherichia coli colonies. These findings provide a safe and green flocculant for efficient microalgae harvesting and spent medium treatment.