Toh, Pey Yi
(2015)
Magnetophoretic Separation Of Microalgae Via Iron Oxide Nanoparticle.
PhD thesis, Universiti Sains Malaysia.
Abstract
Harvesting of microalgae biomass is a crucial step in obtaining the microalgae biomass as biofuel feedstock and also to avoid the secondary water pollution caused by the decomposition of microalgae biomass in the water system.
Magnetophoretic separation is being recognized as a feasible method to harvest the microalgae. It is performed via attachment of iron oxide magnetic nanoparticles (IONPs) on the cell surface in order to impart the magnetic property onto the cells
and hence enable the subsequent collection of cells by using a permanent magnet.
The electrostatic-mediated-attachment mechanism which enables the attachment and
detachment of particle-to-microalgal cell is usually done through a series of pH manipulation. However, the need of pH adjustment onto the microalgae culture medium prohibited the use of this technology in large scale application. Therefore,the surface functionalization of IONPs to form positively charged surface functionalized IONPs (SF-IONPs) is carried out in order to overcome the drawback associated with pH manipulation. This study looked into the characterization of the prepared SF-IONPs, the modeling of particle-to-microalgal cell interaction, the separation kinetic in low gradient magnetic separation (LGMS), and its feasibility on
water treatment and biofuel production. The colloidally stable positively charged SFIONPs which were prepared via immobilized-on approach promote effective electrostatic attachment of SF-IONPs on the freshwater Chlorella vulgaris. The surface functionalization using poly(diallyldimethylammonium chloride) (PDDA)was chosen over chitosan since its surface charge are not pH dependent. A high cell separation efficiency of > 97 % was obtained in all range of pH tested and the oil
quality from the harvested biomass was not affected. The kinetic study indicated that the cell separation is initiated via particle-to-microalgal cell aggregation during incubation followed by field-induced-aggregation under magnetic field in LGMS with ∇B < 80 T/m. Extended Derjaguin-Landau-Vewey-Overbeek (XDLVO)analysis employed to predict the interaction between SF-IONPs and microalgal cells took into account the van der Waals (vdW), ES and Lewis acid-base (AB) interactions. The ES interaction governed the net interaction between cell and SFIONPs in freshwater media while the AB and vdW interactions play a dominant role in seawater. XDLVO predicted effective attachment of SF-IONPs onto cell surface with a secondary minimum of -3.12 kT, which is in accordance with the experimental result. This gave an insight on the strategy of particle detachment from
cell for reuse. In overall, the performance of SF-IONPs is strongly depending on the particle stability, molecular weight (MW) of PDDA, particle concentration, and the microalgae species. The SF-IONPs coated by very low MW PDDA at dosage of 100 g PDDA/g IONPs formed the most colloidally stable suspension and it enabled the
separation of C. vulgaris at almost 100 % efficiency with SF-IONPs concentration of ≥ 50 mg/L. The light shading effect and cell agglomeration were the main toxic
effect of SF-IONPs (PDDAvl) toward the growth of C. vulgaris. This technology was proven effective and cost feasible in fishpond water treatment. A cell separation
efficiency of 90 % was achieved and at water treatment cost of USD$0.15/m3 with a dosage of 0.519 g SF-IONPs/g dry biomass under the LGMS. In biofuel production,
further improvement is required to meet the economic feasibility.
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