Magnetic-Nanoflocculant-Assisted Water–Nonpolar Solvent Interface Sieve for Microalgae Harvesting

Abstract

Exploitation of magnetic flocculants is regarded as a very promising energy-saving approach to microalgae harvesting. However, its practical applicability remains limited, mainly because of the problem of the postharvest separation of magnetic flocculants from microalgal flocs, which is crucial both for magnetic-flocculant recycling and high-purity microalgal biomasses, but which is also a very challenging and energy-consuming step. In the present study, we designed magnetic nanoflocculants dually functionalizable by two different organosilane compounds, (3-aminopropyl)triethoxysilane (APTES) and octyltriethoxysilane (OTES), which flocculate negatively charged microalgae and are readily detachable at the water-nonpolar organic solvent (NOS) interface only by application of an external magnetic field. APTES functionalization imparts a positive zeta potential charge (29.6 mV) to magnetic nanoflocculants, thereby enabling microalgae flocculation with 98.5% harvesting efficiency (with a dosage of 1.6 g of dMNF/g of cells). OTES functionalization imparts lipophilicity to magnetic nanoflocculants to make them compatible with NOS, thus effecting efficient separation of magnetic flocculants passing through the water-NOS interface sieve from hydrophilic microalgae. Our new energy-saving approach to microalgae harvesting concentrates microalgal cultures (∼1.5 g/L) up to 60 g/L, which can be directly connected to the following process of NOS-assisted wet lipid extraction or biodiesel production, and therefore provides, by simplifying multiple downstream processes, a great potential cost reduction in microalgae-based biorefinement.

Smart and Reusable Biopolymer Nanocomposite for Simultaneous Microalgal Biomass Harvesting and Disruption: Integrated Downstream Processing for a Sustainable Biorefinery

“…This is evident from the higher zeta potential values of the synthesized CTC (43.6 ± 1.2 mV) and MNCs (54.7 ± 2.5 mv), as compared to chitosan (9.1 ± 0.4 mV). The obtained higher zeta potential illustrates the presence of increased surface charge on nanocomposites, which is adequate for complete flocculation of microalgal cells (zeta potential, −14.1 ± 0.7 mV), without adjusting the culture pH (7 ± 0.2) . This indicates that the primary mechanism of cell separation is due to electrostatic attraction, which is corroborated by correlating the zeta potential values with flocculant concentration (Figure C).…”

“…With the increasing global energy demands and its associated impact on climate have motivated the scientific communities to provide innovative solutions for the development of green, renewable, and economically feasible biofuels. In recent years, microalgae have emerged as a sustainable feedstock for the production of biofuels and high-value carotenoids, due to their inherent abilities including high growth rate, CO 2 sequestration, and effective land utilization, as compared to terrestrial energy crops. − However, the production of biofuels and carotenoids from microalgal biomass is still not economically viable, owing to the significant fossil energy inputs required for downstream processes. , For instance, the cost of harvesting microalgal biomass is estimated to be 20–30% of the total production cost. , Moreover, intense energy inputs are required for further downstream processing of biomass involving cell disruption, product extraction and purification. , Hence, the development of an integrated process which concomitantly addresses subsequent downstream step is expected to improve the cost-effectiveness of microalgal products.…”

An Overview of Surface‐Functionalized Magnetic Nanoparticles: Preparation and Application for Wastewater Treatment

“…Lee et al. coated SiO 2 on the outer layer of Fe 3 O 4 nanoparticles with TEOS as a silicon source firstly, followed by adding (3‐aminopropyl) triethoxysilane (APTES) and octyltriethoxysilane (OTES) into the mixed solution, then the surface‐modified magnetic nano‐adsorbed material (Fe 3 O 4 @SiO 2 @APTES/OTES) was prepared, the preparation process is shown in Figure . The prepared magnetic adsorption material is mainly used for the removal of microalgae in water.…”

Flocculation Performance and Kinetics of Magnetic Polyacrylamide Microsphere under Different Magnetic Field Strengths

“…[1][2][3]. Microalgae can be harvested by using magnetic nanocomposites, and 90% or above cell recovery can be achieved within 5 minutes [4][5][6][7]. In a short time, magnetic flocculants can remove heavy metal ions with low economic cost [8][9][10][11].…”