Application of Fe3O4 coated with modified plant polyphenol to harvest oleaginous microalgae

Abstract

Harvesting of Chlorella vulgaris was conducted by employing Fe3O4 particles coated with either amino-methylated plant polyphenol (APP) or quaternary ammonium modified PP (QPP). The magnetic composites were characterized using X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and zeta potential. The harvesting efficiency (HE) of the two composites was compared using different parameters, including dosage, initial pH, algal organic matter (AOM) and cell density. Compared with the APP (N) coated Fe3O4 particles, the QPP (N+) was coated onto Fe3O4 by the NO bond. TGA showed that the weight percentages of APP and QPP coated onto Fe3O4 surface were 4.5% and 5.6%, respectively. Compared with the isoelectric point 7.0 of Fe3O4/APP, the isoelectric point of Fe3O4/QPP increased from 7.0 to 13.5. Fe3O4/QPP can not only achieve 91.0% HE of C. vulgaris (3.10 g dry mass/L), but can also overcome the obstacles posed by AOM, high culture pH and high culture biomass. Fe3O4/APP was more suitable in acidic solutions (pH ≤ 6.0) and with lower cell densities (<~109 cells/L), and it could overcome the disturbance of AOM at higher dosages (>10.0 g/L). Fe3O4 can be recovered from algal aggregates by ultrasonication at more than a 97.0% recovery efficiency. The re-coated composites can also achieve 71.9% HE for Fe3O4/APP and 76.3% HE for Fe3O4/QPP after the tenth cycle. Both of the two composites can achieve satisfactory harvesting, while Fe3O4/QPP was more competitive in harvesting oleaginous microalgae from the original culture media.