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