# Flocculation Harvesting Techniques for Microalgae: A Review
## 3 Bio-Flocculation
### Alga  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{2}{c}{**Flocculant (Dosage)**} & \multicolumn{2}{c}{**Alga (Cell Density, Volume or Amount)**} & \multicolumn{2}{c}{**Optimal Harvesting**} & \multicolumn{1}{c}{**Ref.**} \\ \hline \multirow{5}{*}{Fungus} & _A. fumigatus_ & C. protothecodes & \(\sim\)90\% @ 24 h & [47] \\ \cline{2-5}  & _A. fumigatus_ (1.5-2.0 \(\times\) 10\({}^{7}\) spores/L) & _S. quadranta_ (5-8 \(\times\) 10\({}^{8}\) cell/mL) & \(\sim\)97\% @ 48 h & [49] \\ \cline{2-5}  & _A. fumigatus_ & _T. suecia_ & \(\sim\)90\% @ 24 h & [47] \\ \cline{2-5}  & _A. lentulus_ (1.0 \(\times\) 10\({}^{6}\) spores/mL) & _Chroococcus_ sp. (1.58 g/L) & \(\sim\)100\% @ 24 h & [48] \\ \cline{2-5}  & _Penicillium_ cells (1.92 g) & _Chlorella_ sp. (3.84 g) & \(\sim\)98\% @ 25 h & [50] \\ \cline{2-5}  & _Penicillium_ spores (1.1 \(\times\) 10\({}^{4}\) cells/mL) & _Chlorella_ sp. (3.84 g) & \(\sim\)99\% @ 28 h & [50] \\ \hline \multirow{5}{*}{Yeast} & Extracellular protein of _S. humans_ (0.1 g/L) & _C. reinhardtii_ (10 mL) & 95\% @ 3 h & [51] \\ \cline{2-5}  & Extracellular protein of _S. humans_ (0.1 g/L) & _Picachlor_ sp. (10 mL) & 75\% @ 3 h & [51] \\ \cline{2-5}  & _S. humans_ (1:1, \(\
u\)/\(\
u\)) & _C. reinhardtii_ (10 mL) & 80\% @ 6 h & [51] \\ \cline{2-5}  & _S. humans_ (1:1, \(\
u\)/\(\
u\)) & _Picachlor_ sp. (10 mL) & 60\% @ 6 h & [51] \\ \cline{2-5}  & _S. pastoriunas_ (0.4 mg/g cell) & _C. vulgaris_ (5 g/L) & 90\% @ 70 min & [45] \\ \hline \multirow{5}{*}{Bacterium} & _Flaroobacterium, Terrimonus, and Sphingobacterium_ & _C. vulgaris_ (6 \(\times\) 10\({}^{6}\) cells/mL) & 94\% @ 24 h & [52] \\ \cline{2-5}  & Bio-flocculent secreted from _S. silvestris_ & _N. ocanica_ DUT01 & 90\% @ 10 min & [53] \\ \cline{1-1} \cline{2-5}  & W01 (3.1, \(\
u\)/\(\
u\)) & _S. obliquus_ FSP-3 (10 mL) & 83\% @ 30 min & [39] \\ \cline{1-1} \cline{2-5}  & _S. obliquus_ AS-6-1 (1%, \(\
u\)/\(\
u\)) & _S. obliquus_ FSP-3 (10 mL) & 97\% @ 4 h & [54] \\ \cline{1-1} \cline{2-5}  & Exudates-rich spent media of C. cf. & _Penicolinoprosum_ (1:1, \(\
u\)/\(\
u\)) & _S. ellipsoidatus_ (15 mL) & 100\% @ 5 min & [14] \\ \cline{1-1} \cline{2-5}  & _Phrutidium_ sp. & _Chlorella_ sp. & 100\% @ 5 min & [14] \\ \hline \hline \end{tabular}
\end{table}
Table 2: Comparison of bio-flocculation techniques for algae harvesting.  
extracellular proteins of anaerobically grown yeast _Saccharomyces bayanus_. The yeast whole cells showed only moderate harvesting efficiencies of 80% and 60% for _C. reinhardtii_ and _Picochlorum_ sp., respectively, after 90 min treatment, albeit at high mixing ratios (1:1). Interestingly, treatment with a relatively low concentration of extracellular yeast proteins (0.1 g/L), led to significant increase in the flocculation efficiencies to 95% and 75%, respectively, for the former and latter algal species [51]. Chemically modified autolsyates of _S. cerevisiae_ (a by-product of the brewing industry) could exhibit high harvesting efficiency of over 90% when applied to _C. vulgaris_ at a dosage of 0.4 mg/g cell [45].  
The algae harvesting process using either yeast whole cells or their extracellular proteins appears to be environmentally friendly. However, extensive research on the technical feasibility of the use of other biofuel algal strains and the availability of low-cost yeast products is required for practical process development.