# Harvesting Microalgae Biomass Using Magnetic Nanoparticles from Iron-Rich Particulate Material

## TL;DR

This paper explores using magnetic nanoparticles from iron-rich material to efficiently harvest microalgae, comparing naked and tannin-functionalized particles.

## Contribution

The study is the first to investigate magnetic nanoparticles derived from particulate matter for microalgae harvesting.

## Key findings

- Naked magnetic nanoparticles achieved 86% harvesting efficiency at optimal conditions.
- Tannin-functionalized nanoparticles showed improved reuse, lasting up to 7 cycles.
- Both nanoparticle types had similar harvesting efficiency at pH 10.

## Abstract

Using magnetic nanoparticles
for efficient microalgae harvesting
has shown promising results with enhanced harvesting efficiency within
a reduced time frame. However, the cost of nanoparticle synthesis
presents a potential constraint the widespread implementation of
this technique. In this way, this work investigated, for the first
time, the efficacy of magnetic nanoparticles (MNPs) derived from particulate
matter for harvesting microalgae (Chlorella sp.) both naked and functionalized with commercial tannin. The nanoparticles
were characterized using X-ray diffraction (XRD), transmission electron
microscopy (TEM), scanning electron microscopy (SEM), energy dispersive
X-ray spectroscopy (EDS), Fourier transform infrared (FTIR), and zeta
potential. The MNPs present in the particulate material were magnetite
with an estimated size (based on 1000 particles) of around 30.5 ±
9.56 nm. Harvesting efficiency (HE %) was optimized using full factorial
experiments, in which the most influential variables (pH and MNPs
concentration) were combined at different levels, achieving optimal
harvesting efficiency. The MNPs (naked) exhibited higher harvesting
efficiency (HE % = 86%; MNPs concentration = 1250 mg. L–1; pH = 3) than functionalized nanoparticles (HE % = 77%; MNP-TANs
concentration = 1100 mg/L; pH = 3.5); however, a higher MNPs concentration
was necessary in a lower pH. The functionalization contributed to
particle stabilization, increasing its reuse cycles from 3 (MNSs)
to 7 cycles (MNP-TANs). At pH 10 (the final pH of the microalgae cultivation),
both exhibited a similar HE % of 60%.