Optimizing magnetic flocculation of Chlorella sp. using magnetite nanoparticles functionalized with tannin from Rhizophora mangle.

Microalgae biomass is considered a rich source of biomolecules and can be applied in different ways, such as in biofuel production, which includes biodiesel, biogas, and biochar. However, the complex and costly harvesting step can impair their industrial potential. To improve harvesting, tannins are highly applied flocculants for microalgae flocculation but stay attached to the microalgae biomass after harvesting, which is not interesting for some applications. This issue can be solved using associated tannins with magnetic nanoparticles (MNPs). Thus, we synthesized (chemical precipitation) and functionalized MNPs with tannin from Rhizophora mangle and applied them to harvest Chlorella sp. The functionalized MNPs (MNP-TNs) were characterized using X-ray diffraction (XDR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray (EDS), Fourier transform infrared (FTIR), and Zeta potential. At the optimum point, the adsorbent achieved a HE% of 92.6% (MNP-TNs concentration = 1000 mg L; pH = 4), maintaining this efficiency during six reuse cycles. The Langmuir isotherm model adjusted best to the data, indicating monolayer adsorption. The process was considered exothermic, favorable, and spontaneous. These results make this material a good candidate for application in larger scales of microalgae harvesting. The high harvesting efficiency, which is particularly impressive given the short time it was achieved in, and the possibility of reusing the particles for several cycles are essential indicators of harvesting optimization; however, some feasibility studies still need to be carried out.