## 3 Results and Discussion
### Effect of the Culture Conditions on the Pollutant Elimination
#### 3.2.5 Fate of CBZ  
Besides studying the removal of the considered pharmaceutical compound, it is very important to investigate and determine the mechanism involved in the elimination of this molecule. Generally, different mechanisms such as biosorption, accumulation, and biotransformation are involved in the removal of organic pollutants [56; 57]. However, they cannot be clearly distinguished since, for example, live cells can also degrade adsorbed pollutants by intracellular mechanisms [58]. In an effort to understand the mechanisms involved in the removal of CBZ by _A. braunii_, it is important to assess the transformation products. The first insights emerged in the HPLC chromatograms (obtained by successive analysis), which showed the presence of a new peak corresponding to an extracellular compound produced by the algae, the concentration of which increased in parallel to the decrease of CBZ. Being identified at the same wavelength, this exhibited a shorter retention time (3 min, while the retention time of CBZ is 18 min). As a consequence, this seemed to indicate the possible biotransformation of CBZ into metabolites and can be considered as an indicator of the biodegradation process. To confirm this result and better analyze the fate and the mechanisms of elimination of CBZ by _A. braunii_, cells were burst under high pressure and then imaged to ensure the complete bursting of the cells so that the CBZ accumulated in the cells, if any, was released in the medium and easy to quantify by HPLC analysis. Figure 5 shows the magnified images of the cells with the elongated shaped _A. braunii_ before pressure treatment and the randomly shaped destroyed cells after the cell burst. This also makes clear, as shown in Figure 5, the asexual mode and binary fission of _A. braunii_ reproduction in the presence of the target compound. HLPC analysis of the liquid phase after _A. braunii_ bursting showed that a high quantity of eliminated CBZ was recovered into the medium. Figure 6 gives a comparison of the CBZ concentrations determined in burst and non-burst cells cultured in BB and PP media. It can clearly be concluded  
Figure 5: Magnified images of _A. braunii_, (**a**) non-burst, where the asexual reproduction of binary fission is shown in the circle, and (**b**) burst cells. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Initial Concentration of** & **Initial Concentration of** & **CBZ \% of Elimination** & **CBZ \% of Elimination** \\
**CBZ** & _A. Braunii_ (**C\({}_{\textbf{i}}\)**)** & **in PP Medium** & **in BB Medium** \\ \hline
2.5 mg/L & \(10^{4}\) cells/mL & 74.8\% & 80.0\% \\
2.5 mg/L & \(10^{5}\) cells/mL & 79.2\% & 87.6\% \\
10 mg/L & \(10^{4}\) cells/mL & 61.0\% & 70.0\% \\
10 mg/L & \(10^{5}\) cells/mL & 66.0\% & 77.0\% \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Removal yield of CBZ determined by HPLC for an initial CBZ content between 2.5 and 10 mg/L, and an inoculum concentration between \(10^{4}\) and \(10^{5}\) cells/mL after 60 days. from this figure that the bioaccumulation of CBZ in the cells played a key role in the removal of this molecule by _A. braunii_. However, it could also be observed that the total amount of CBZ found in the solution even after the algal bursting only corresponded to 80% of the initial CBZ concentration, which was 2.5 mg/L. Surprisingly, the lowest amount of CBZ recovered in the medium corresponded to the case of the highest CBZ elimination, i.e., in the BB medium starting with 10\({}^{5}\) cells/mL of _A. braunii_ and 2.5 mg/L of CBZ. Moreover, the HPLC data analysis also highlighted that the surface area of both the CBZ and the other peak increased simultaneously in both media after bursting _A. braunii_ cells and that the area of the second peak was maximized in the BB medium starting with 10\({}^{5}\) cells/mL of _A. braunii_ and 2.5 mg/L of CBZ (data not shown).