Magnetic Flocculant Research Articles

Magnetic nanoparticles grafted with amino-riched dendrimer as magnetic flocculant for efficient harvesting of oleaginous microalgae

Magnetic iron oxide (Fe3O4) nanoparticles (MNPs) was assigned to coat with amino-riched polyamidoamine (PAMAM) dendrimer (Fe3O4@PAMAM; Gn-dMNPs, n=0, 1, 2, 3) and employed in the magnetic harvesting of oleaginous Chlorella sp. HQ due to the highly positive branched structure. The coating process was realized by stepwise grafting which encompasses Michael addition and amidation reaction. Amino-micromolecular amino acids were used to modify Fe3O4 MNPs as control groups to investigate the difference of microalgal harvesting between modification with polymer and micromolecule firstly. The results showed that the coating of highly positive branched PAMAM dendrimer could dramatically promote the adsorption between algae cells and nanoparticles, leading to a large drop of nanoparticles dosage, compared with amino acid (AA)-modified Fe3O4 MNPs (Fe3O4@AA). The influence of polymer coating thickness which is an unclear factor on harvesting was explored initially, suggesting that the harvesting efficiency was positively correlated with the coating thickness of PAMAM dendrimer and reached over 95% within 2min when using 80mgL−1 G3-dMNPs at pH 8.0. Moreover, the harvesting efficiency rose dramatically when pH decreased from 10.0 to 4.0 for G0∼G2-dMNPs, while the high efficiency for G3-dMNPs could be maintained in a wide pH range for the amino-riched branched structure. It can be attributed to increased electrostatic attraction and bridging flocculation caused by abundant active sites of the highly positive branched network on Fe3O4 MNPs. It can be expected that this novel magnetic flocculant has the potential to be applied to harvesting of oleaginous microalgae due to its high efficiency and cycling stability.

Repeated use of stable magnetic flocculant for efficient harvest of oleaginous Chlorella sp.

In the present study, a simple magnetic-particle recycling strategy was developed for harvest of the oleaginous microalga Chlorella sp. KR-1. The method entails the flocculation of microalgal cells and bare-Fe3O4 magnetic particles (bMP) by electrostatic attraction and the subsequent recovery of the bMP from the harvested flocs by electrostatic repulsion below and above the isoelectric points (IEP), respectively. For 10 recycles, the bMP showed 94–99% and 90–97% harvest and recovery efficiencies, respectively. Furthermore, neither the use of bMP nor pH adjustment showed any adverse effect on the microalgal cell growth or the co-existing bacterial species, as confirmed from the subsequent medium-recycling test and denaturing gradient gel electrophoresis (DGGE) analysis.

Magnetic Flocculant for High Efficiency Harvesting of Microalgal Cells

Magnetic flocculant was synthesized for the highly efficient recovery of microalgal cells. The highest flocculation was achieved using the magnetic flocculant synthesized with iron oxide and 0.1 mg/mL cationic polyacrylamide (CPAM). This resulted in a recovery efficiency of more than 95% within 10 min using a dosage of 25 mg/L for Botryococcus braunii and 120 mg/L for Chlorella ellipsoidea. For both species, the adsorption isotherm data fit the Freundlich model better than the Langmuir model, indicating that the adsorption process was a heterogeneous multilayer. The maximum adsorption capacity was 114.8 and 21.4 mg dry cells/mg-particles at pH 7 for B. braunii and C. ellipsoidea, respectively. The primary flocculation mechanism was bridging, which was assisted by the electrostatic interactions between the microalgal cells and the magnetic flocculant under acidic conditions. These results provide new opportunities and challenges for understanding and improving the harvesting of microalgae using magnetic separation.