# Flocculation Harvesting Techniques for Microalgae: A Review
## 7 Conclusions and Future Perspectives
[PERSON], [PERSON], and [PERSON] conceived the concept for the review; [PERSON], [PERSON], [PERSON], and [PERSON] analyzed the existing literature; and [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] wrote and edited the manuscript. This work was supported by the Advanced Biomass R&D Center (ABC) of the Global Frontier Project (ABC-2012M3A6A205388) and the National Research Foundation of Korea (NRF) grant (NRF-2019R1A2C1003463) funded by the Ministry of Science and ICT, Republic of Korea, and the Basic Science Research Program of the National Research Foundation of Korea funded by the Ministry of Education (NRF-2017R1D1A1A09000642), Republic of Korea. This work was also conducted under the framework of the Research and Development Program of the Korea Institute of Energy Research (KIER; B8-2432-04). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Technique** & **Mechanism** & \multicolumn{2}{c}{**Advantages**} & \multicolumn{2}{c}{**Disadvantages**} \\ \hline \multirow{3}{*}{Auto-flocculation} & Spontaneous aggregation and sedimentation under stress & \(\bullet\) & Cheap & \(\bullet\) & Limited to certain algal species \\  & conditions & \(\bullet\) & Eco-friendly & & \\  & & conditions & \(\bullet\) & No chemical flocculant & \(\bullet\) & Time-consuming \\  & & is required & & \(\bullet\) & Low efficiency \\ \hline \multirow{3}{*}{Bio-flocculation} & Co-pelletization of target algal & \(\bullet\) & Renewable & \(\bullet\) & Species-specific \\  & species using bio-flocculants & \(\bullet\) & No chemical flocculant & \(\bullet\) & Biomass contamination \\  & (fungi, bacteria, yeast, algae and their extracellular polymers) & & is required & \(\bullet\) & Environmental concern \\  & & & & & due to flocculant release \\ \hline \multirow{3}{*}{Chemical flocculation} & Charge neutralization, bridging, & \(\bullet\) & Fast & \(\bullet\) & Biomass contamination \\  & and sweeping of algal cells with & \(\bullet\) & Effective & & \(\bullet\) & Fluorescent concern \\  & charged chemicals & \(\bullet\) & Scalable & \(\bullet\) & Efficiency is sensitive to \\ \hline \multirow{3}{*}{Particle-based flocculation} & Charge neutralization and electrostatic bridging with functional nano/macro-particles & \(\bullet\) & Rapid (e.g., magnetic separation) & \(\bullet\) & Expensive manufacturing \\  & & & Multi-functionalities & \(\bullet\) & Limited to \\  & & & for post-processing & & laboratory-scale studies \\  & & & \(\bullet\) & Reusability of flocculant & \\ \hline \multirow{3}{*}{Electrochemical flocculation} & Floc formation using metal ions & \(\bullet\) & Fast & \(\bullet\) & Fouling and short life-time \\  & and charge neutralization by & \(\bullet\) & Suitable for almost all & \(\bullet\) & of electrodes \\ \cline{1-1}  & passing direct electrical current & & types of algae & \(\bullet\) & Biomass contamination by \\ \cline{1-1}  & through electrodes & \(\bullet\) & No chemical is required & \(\bullet\) & Electrical energy demand \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Comparison of five flocculation techniques for algae harvesting.