# Adsorption of Heavy Metals from Low Concentration Solutions onto Dried _Chlamydomonas reinhardtii_
## 3 Results
### Biosorption on Dried Algae
#### 3.2.3 Preliminary Comparison of Adsorption to Living and Dried Algae: Cd(II) Case  
A preliminary comparison between living and dried algae adsorption behaviour was performed on Cd solution, applying the same conditions reported above. Results of the comparison of the adsorption capacity, measured by ICP-OES of the initial and final solution of the living and the dried algae are summarized Table 1.  
After 2 days of contact time, both living and dried algae were able to capture the same Cd amount, i.e., 78% (\(w/w\)) and 76% (\(w/w\)) of the total. However, when the contact time was prolonged for 4 days, the living algae were able to capture a larger amount of ions, up to 91% (\(w/w\)), while in the dried one, Cd adsorption is even lower (76% (\(w/w\)) and 63% (\(w/w\)) at 2 and 4 days of contact time, respectively).  
After the contact reaction, the living cells were freeze-dried and characterized by FT-IR-ATR analysis (Figure 12).  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Ion**} & \multirow{2}{*}{
\begin{tabular}{c} **Initial Metal** \\ **Concentration (mg/L)** \\ \end{tabular} } & \multirow{2}{*}{**pH**} & \multirow{2}{*}{**Contact Time**} & \multicolumn{2}{c}{**Dried Algae Adsorption**} & \multicolumn{2}{c}{**Living Algae Adsorption**} \\ \cline{4-7}  & & & & **mg/L** & **\% (\(w/w\))** & **mg/L** & **\% (\(w/w\))** \\ \hline \multirow{2}{*}{Cd(II)} & \multirow{2}{*}{0.2 \(\pm\) 0.002} & \multirow{2}{*}{6} & 2 days & 0.151 \(\pm\) 0.001 & 76 & 0.156 \(\pm\) 0.001 & 78 \\ \cline{3-7}  & & & 4 days & 0.125 \(\pm\) 0.001 & 63 & 0.182 \(\pm\) 0.001 & 91 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Comparison between Cd adsorption in living and dried algae.  
Figure 11: SEM pictures of the microcalga before and after metal adsorption in multi-ion solutions at different pH magnifications: (**a**) 2.50 KX and (**b**) 5.00 KX.  
No significant differences are present in the high frequency region of the living and the dried microalga after adsorption. The band centred at 1244 cm\({}^{-1}\) appears to be less intense than the pristine one, but more intense than the dried microalga. Also, the low frequency region, around 800 cm\({}^{-1}\), changes following the same behaviour as before: lower intensity than the pristine, and higher intensity than the living microalga.  
The morphology of the living and dried algae before and after Cd capture was analysed by SEM analysis, pictures are reported in Figure 13 at two different magnifications, namely 2.50 KX (above) and 5.00 KX (below). In dried algae (Figure 13b), only the typical effect of the drying process on the cells manifests itself. Similarly, the living algae show signs of cell wall damage [55]; however, in this sample, cells appear slightly smaller, oval-shaped, and less grouped. Also, in this case, EDX analysis (Figure S6) did not evidence any adsorption of Cd ions.  
Figure 12: FTIR-ATR spectra of the living and dried algae after Cd(II) adsorption. Untreated algae spectrum is reported for comparison. Living cells were dried after being contacted with Cd solution.  
Figure 13: SEM pictures of microalga (**a**) before adsorption and after Cd(II) adsorption on (**b**) dried form and (**c**) living form.