## 3 Results and Discussion
### Effect of the Culture Conditions on the Pollutant Elimination  
#### 3.2.1 Effect of Culture Medium  
The effect of the composition of culture media used for the _A. braunii_ growth on the removal of CBZ was investigated. Figure 2 plots the time profiles for the residual CBZ concentration for both of the investigated culture media and an initial inoculum and pollutant concentration of \(10^{4}\) cells/mL and 10 mg/L, respectively. As shown in this figure, the evolution of CBZ concentration over time exhibited the same profile in both media. Three phases are really discriminated for both investigated media: first, it was constant or decreased slightly, and then, a steep decrease was reported, followed by a slow decrease of CBZ content. The key difference between BB and PP media was the period at which the steep decrease was reported: it occurred 12 days before in BB than in PP. BB was shown to be more favorable than PP for the CBZ elimination after 60 days of incubation, as a higher removal yield was achieved. For example, with an inoculum concentration of \(10^{4}\) cells/mL and an initial CBZ content of 10 mg/L, this yield was \(70\%\pm 4\) in BB medium, but only \(66\%\pm 3\) in PP. However, the BB medium also led to faster removal. This is in accordance with the results presented previously. _A. braunii_ cell concentration and CBZ elimination increased simultaneously, suggesting that CBZ could be used as a nutritive source by the microalgae, but other explanations can be found. For example, these trends could also be related to a bioaccumulative, biosorptive, or metabolic role of _A. braunii_, as the kinetics of these mechanisms are also proportional to the amount of algae. The results presented here are not unexpected, as algae are known to be able to degrade recalcitrant organic compounds. Indeed, [PERSON] et al. [43] demonstrated the biotransformation of naphthalene and diaryl ethers, complex aromatic pollutants, by _Chlorella_, _Ankistrodesmus_, and _Scenedesmus_ strains. Other studies reported  
Figure 2: Effect of the culture media on CBZ removal for an initial pollutant concentration of 10 mg/L and an initial inoculum concentration of \(10^{4}\) cells/mL. that numerous algal strains induce biotransformation of exogenous steroids or low-molecular-weight phenols [44; 45; 46]. However, to the best of our knowledge, no previous study has demonstrated the removal of CBZ with algae pure cultures. For a better understanding of experimental results, the growth curves and the residual CBZ concentration were plotted together in Figure 2 for each tested culture medium. The obtained data highlights an interaction between these two parameters: the delayed exponential growth phase in PP led to a delayed death phase and to a delayed onset of CBZ elimination. The role of _A. braunii_ in CBZ elimination is, therefore, assured by comparing growth kinetics and the consequent CBZ amount in both culture media. Figure 2 showed a synchronized behavior between the _A. braunii_ cell growth and the residual amount of CBZ. For example, when working at an initial inoculum concentration of \(10^{4}\) cells/mL and an initial CBZ concentration of 10 mg/L, the amount of CBZ at the very beginning of the culture was almost stable during the first five to eight days corresponding to the latent phase of the algae, but this was followed by a rapid decrease of CBZ concentration that took place at the time where the highest cell concentration is attained in both BB and PP. Thus, during the first phase, cells seem to prepare themselves to better assimilate the pollutant, and no appreciable changes in the biomass and CBZ concentration were observed. The improved performance of _A. braunii_ in the removal of the xenobiotic compound becomes effective during the second phase when a rapid increase in the growth rate and pollutant consumption was observed. Finally, the removal of the target pollutant continues during the negative cell-growth period.