Magnetic Fe3O4-polyethyleneimine nanocomposites for efficient harvesting of Chlorella zofingiensis, Chlorella vulgaris, Chlorella sorokiniana, Chlorella ellipsoidea and Botryococcus braunii

A reduction in energy consumption at every stage of the down streaming process is needed to make 3rd generation of biofuels economically viable. In this study, magnetite (Fe3O4) nanoparticles were synthetized by coprecipitation of FeCl2 and FeCl3 in alkaline medium at two different temperatures. The particle sizes were 11.5 +/- 4 and 9.5 +/- 4 nm for the nanoparticles prepared at 80 degrees C and 25 degrees C, respectively. The adsorption of polyethyleneimine (PEI) onto Fe3O4 was studied by equilibrium batch measurements. A mono-layer absorption of PEI was found. The Fe3O4-PEI nanocomposites had a positive zeta potential, which decreased with increasing pH of the solution. The nanocomposites were used for magnetic harvesting of negatively charged Chlorella zofingiensis, Chlorella vulgaris, Chlorella sorokiniana, Chlorella ellipsoidea and Botryococcus braunii microalgae strains. Upon dosage of 200 mg/L of Fe3O4-PEI harvesting efficiencies of 68-97% were achieved at pH 4 within 1 min. The harvesting efficiency decreased with increasing pH of the suspension. The results demonstrate that Fe3O4 nanoparticles synthesized at the lower temperature (25 degrees C) could be used for an efficient magnetic harvesting of different microalgae strains. The lower synthesis temperature may thereby contribute to the cost reduction of microalgae harvesting.