# Flocculation Harvesting Techniques for Microalgae: A Review
## 5 Particle-Based Flocculation
### Magnetic Particle  
Magnetic nanoparticles (MNPs) have played innovative roles in different biomedical, biotechnological, and environmental applications. Solid-liquid separation using MNPs is one of the most promising strategies in wastewater treatment [115]. Regarding algae separation, MNPs were first applied to remove harmful algae in lakes [116]. Later, as algal biomass became a more popular feedstock for various applications, including biofuels production, they were used for the recovery of algae from mass-culture systems [117]. Magnetic-particle-based flocculation has a powerful advantage in terms of separation time as MNP-attached flocs can be easily manipulated by an external magnetic field (Figure 5). Since 2010, varieties of freshwater and marine algal species have been successfully harvested via flocculation processes with magnetic particles for biofuel production (see Table 4). Despite the high manufacturing costs of MNPs, the reuse of culture supernatant (after magnetic separation) as the culture medium and the recycling of MNPs was attempted to decrease the cost of biomass and biofuel production [107; 118]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Kind** & **Flecculant** & **Dosage** & **Alga (Cell Density)** & \begin{tabular}{c} **Optimal** \\ **Harvesting** \\ \end{tabular} & **Ref.** \\ \hline \multirow{7}{*}{\begin{tabular}{c} Aminoclay-based \\ nanoparticle \\ \end{tabular} } & AI-AC & 0.6 g/L & _Chloella_ sp. KR-1 (1.7 g/L) & 100\% @ 30 min & [99] \\ \cline{2-5}  & AC-conjugated TiO\({}_{2}\) & 3.0 g/L & _Chloella_ sp. KR-1 (1.5 g/L) & -85\% @ 10 min & [100] \\ \cline{2-5}  & AC-induced humic acid & 5.0 g/L & _Chloella_ sp. (1.3 g/L) & -100\% @ 30 min & [101] \\ \cline{2-5}  & AC-templated nZVI & 19.1 g/L & _Chloella_ sp. KR-1 (1.5 g/L) & -100\% @ 3 min & [102] \\ \cline{2-5}  & APTES-coated BaFe\({}_{12}\)O\({}_{19}\) & 2.3 g/g cell & _Chloella_ sp. KR-1 & 99\% @ 3 min & [103] \\ \cline{2-5}  & MgAC-Fe\({}_{3}\)O\({}_{4}\) hybrid composites & 4.7 g/L & _Chloella_ sp. KR-1 (1.75 g/L) & 99\% @ 10 min & [104] \\ \cline{2-5}  & MgAC-Fe\({}_{3}\)O\({}_{4}\) hybrid composites & 4.3 g/L & _S. obliquus_ (2.0 g/L) & 99\% @ 10 min & [104] \\ \cline{2-5}  & Mg-APTES & 0.6 g/L & _Chloella_ sp. KR-1 (1.7 g/L) & 100\% @ 30 min & [99] \\ \cline{2-5}  & Mg-APTES & 1.0 g/L & _C. vulgaris_ (1.0 g/L) & 97\% @ 125 min & [98] \\ \cline{2-5}  & Mg-AC and Ce-AC & 0.2 g/L & Cyanobacteria & -100\% @ 60 min & [105] \\ \hline \multirow{7}{*}{\begin{tabular}{c} Magnetic particle \\ Magnetic particle \\ \end{tabular} } & Fe\({}_{3}\)O\({}_{4}\) nanoparticle & \begin{tabular}{c} 55.9 mg cell/mg \\ particles \\ \end{tabular} & _B. braunii_ & 98\% @ 1 min & [106] \\ \cline{2-5}  & Fe\({}_{3}\)O\({}_{4}\) nanoparticle & \
\begin{tabular}{c} 5.8 mg cell/mg \\ particles \\ \end{tabular} & _C. ellipsooida_ & 98\% @ 1 min & [106] \\ \cline{2-5}  & Fe\({}_{3}\)O\({}_{4}\) nanoparticle & 0.12 g/L & _N. maritima_ & 95\% @ 4 min & [107] \\ \cline{2-5}  & Fe\({}_{3}\)O\({}_{4}\) magnetic particle & 10 g/g cell & _Chloella_ sp. KR-1 & 99\% @ 1 min & [108] \\ \cline{2-5}  & Fe\({}_{3}\)O\({}_{4}\)-embedded carbon &
\begin{tabular}{c} -25 g/L \\ microparticle \\ \end{tabular} & _Chloella_ sp. KR-1 (-2 g/L) & 99\% @ 1 min & [109] \\ \cline{2-5}  & Fe\({}_{3}\)O\({}_{4}\)-PEI nanocomposite & 0.02 g/L & _C. ellipsooida_ (0.75 g/L) & 97\% @ 2 min & [110] \\ \cline{2-5}  & PEI-coated Fe\({}_{3}\)O\({}_{4}\) & 0.2 g/L & _S. dimorphus_ (1.8 g/L) & 82.7\% @ 3 min & [111] \\ \cline{2-5}  & Fe\({}_{3}\)O\({}_{4}\)-carbon-microparticle & 10 g/L & _Chloella_ sp. KR-1 (2.0 g/L) & 99\% @ 1 min & [109] \\ \cline{2-5}  & Chitosan-Fe\({}_{3}\)O\({}_{4}\) composite & 1.4 g/L & _Chloella_ sp. KR-1 (1.0 g/L) & -99\% @ 5 min & [112] \\ \cline{2-5}  & Chitosan-coated Fe\({}_{3}\)O\({}_{4}\)-TiO\({}_{2}\) & 0.07 g/g cell & _C. minutilsima_ (3.0 g/L) & 98\% @ 2 min & [113] \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of particle-based flocculants for algae harvesting.