# Flocculation Harvesting Techniques for Microalgae: A Review
## 4 Chemical Flocculation
### Inorganic Flocculant
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Flocculant (Dosage)**} & \multirow{2}{*}{**Alga (Cell Density or Volume)**} & **Optimal** & \multirow{2}{*}{**Ref.**} \\  & & & \\  & & & \\ \hline Al\({}_{2}\)(SO\({}_{4}\))\({}_{3}\) (1.2 g/L) & _Tetraselmis_ sp. KCTC12236 BP (3 g/L) & 86\% @ 30 min & [64] \\ \hline Al\({}_{2}\)(SO\({}_{4}\))\({}_{3}\) (152 mg/L) & _Chlorells_ sp. (0.12 g/L) & 100\% @ 60 min & [65] \\ \hline Al\({}_{2}\)(SO\({}_{4}\))\({}_{3}\) (180 mg/L) & _Scenedesmus_ sp. (0.20 g/L) & 90\% @ 20 min & [66] \\ \hline Al\({}_{2}\)(SO\({}_{4}\))\({}_{3}\) (20 mg/L) & C. _reinhardtii_ (0.31 g/L) & 90\% @ 20 min & [66] \\ \hline Al\({}_{2}\)(SO\({}_{4}\))\({}_{3}\) (438.1 uM) & _N.__culata_ (1.7 g/L) & 92\% @ 320 min & [32] \\ \hline Al\({}_{2}\)(SO\({}_{4}\))\({}_{3}\) (50 mg/L) & _S.__limacimum_ (0.93 g/L) & 90\% @ 20 min & [66] \\ \hline CaO (60 mg/L) & C. _valgaris_ (1.5 g/L) & 85\% @ 5 min & [67] \\ \hline CaCO\({}_{3}\)-rich eggshell (80 mg/L) & C. _valgaris_ (2.3 g/L) & 99\% @ 20 min & [68] \\ \hline FeCl\({}_{3}\) (0.4 g/L) & _N.__culata_ (50 mL) & 94\% @ 180 min & [69] \\ \hline FeCl\({}_{3}\) (143 mg/L) & _Chlorells_ sp. (0.12 g/L) & 100\% @ 40 min & [65] \\ \hline FeCl\({}_{3}\) (438.1 uM) & _N.__culata_ (2.2 g/L) & 78\% @ 320 min & [32] \\ \hline Fe\({}_{2}\)(SO\({}_{4}\))\({}_{3}\) (0.6 g/L) & _N.__culata_ (50 mL) & 87\% @ 180 min & [69] \\ \hline Fe\({}_{2}\)(SO\({}_{4}\))\({}_{3}\) (1.0 g/L) & _Chlorells_ sp. KR-1 (1.52 g/L) & 98\% @ 30 min & [70] \\ \hline Mg(OH)\({}_{2}\) (1 mM) & _Chlorells_ sp. (0.1 g/L) & 90\% @ 30 min & [71] \\ \hline Cationic inulin (60 mg/L) & _Botryococcus_ sp. & 89\% @ 15 min & [72] \\ \hline Cationic starches (0.01 g/L) & _S.__dimorplus_ (0.12 g/L) & 95\% @ 90 min & [73] \\ \hline Cationic starches (1.4:l, w/w) & _S.__obliquus_ & 90\% @ 60 min & [74] \\ \hline Cationic starches (119 mg/g cell) & _B.__brantii_ (0.62 g/L) & 94\% @ 20 min & [75] \\ \hline Cationic starches (50 mg/L) & _S.__limacimum_ (0.93 g/L) & 90\% @ 20 min & [66] \\ \hline Cationic starches (7.1 mg/L) & C. _valgaris_ (0.75 g/L) & 90\% @ 120 min & [76] \\ \hline Cationic starches (89 mg/g cell) & C. _pyrenodiosa_ (1.02 g/L) & 96\% @ 20 min & [75] \\ \hline Chitosan (10 mg/g cell) & _C.__sorbinimia_ & 99\% @ 45 min & [77] \\ \hline Chitosan (120 mg/L) & _C.__valgaris_ (1 g/L) & 99\% @ 3 min & [78] \\ \hline Chitosan (40 mg/L) & _Scenedesmus_ sp. A1 & 82\% @ 60 min & [12] \\ \hline Chitosan (30 mg/L) & _Chlorells_ sp. (\(3\times 10^{7}\) cells/mL) & 97\% @ 60 min & [61] \\ \hline Chitosan (30 mg/L) + sodium & _S.__obliquus_ & 86\% @ 60 min & [40] \\ \hline Epichlorohydrin-n,n- & _Scenedesmus_ sp. (100 mL) & \textgreater{}90\% @ 30 min & [79] \\ (8 mg/L) & _M.__arenginos_ (\(1\times 10^{9}\) cells/L) & 97\% @ 120 min & [80] \\ \hline Modified tannin (210 mg/L) & _Scenedesmus_ sp. & 97\% @ 40 min & [81] \\ \hline Modified tannin (10 mg/L) & _N.__culata_ (400 mg/L) & 98\% @ 30 min & [82] \\ \hline Poly-L-lysine (70-150 kDa, 0.5 mg/L) & _C.__ellipsoidea_ (1 g/L) & 98\% @ 75 min & [83] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison of inorganic and organic chemical flocculants for algae harvesting. Ferric sulfate (Fe\({}_{2}\)(SO\({}_{4}\))\({}_{3}\)) and ferric chloride (FeCl\({}_{3}\)) have been used for algae harvesting as well. Harvesting efficiencies of 93.8% and 87.3% were reported for marine alga \(N\). _oculata_ using 0.4 g/L Fe\({}_{2}\)(SO\({}_{4}\))\({}_{3}\) and 0.6 g/L FeCl\({}_{3}\), respectively, after treatment for 180 min [69]. However, Fe\({}_{2}\)(SO\({}_{4}\))\({}_{3}\) is not preferred for large-scale applications due to its strong and corrosive reactivity. [64]. This challenge could be resolved if Fe\({}_{2}\)(SO\({}_{4}\))\({}_{3}\) is efficiently removed and recycled after being used for algae harvesting. Recently, [PERSON] et al.