## 3 Results and Discussion
### Effect of CBZ on the A. brauntii Growth
This showed clearly that the ratio between inoculum and CBZ concentrations played a key role in the _A. braunii_ growth. The differences between BB and PP could be related to a possible interaction of CBZ with the proteosepitone in PP, as CBZ is known to interact with proteins [38]. This would lead to a decrease in the amount of the proteins available for the algae to grow, and consequently to a weaker growth rate. However, no interaction between the proteosepitone medium and CBZ was found using HPLC, although this could vanish in the acetonitrile/water eluent. Another explanation is that CBZ is toxic for _A. braunii_, but that CBZ assimilation is less rapid in the presence of EDTA (nutritive source of C and N in BB), which also accelerated algae growth under these conditions. Conversely, the rapid algae death that followed could be attributed to a toxic effect of CBZ under EDTA limitation. This contradicts the results of [PERSON] et al. [23], who reported no toxicity of CBZ on _A. braunii_, but used a far lower initial concentration of CBZ, about \(2.1\times 10^{-6}\) g/L. Finally, for the efficient and rapid growth of _A. braunii_ microalgae, experimental data shows that PP should be preferred, but in the presence of CBZ, BB should be used because of the evidenced strong interaction between CBZ and algae growth. Consequently, the influence of the initial CBZ concentration was investigated for both media and initial inoculum concentrations. Two initial CBZ contents (2.5 mg/L and, 10 mg/L, respectively) were investigated in this work. Experimental results showed that, for all the experiments, a higher concentration of the pollutant further shortened the exponential growth phase and lowered the obtained maximum algae concentration. Indeed, a high initial CBZ content forwarded the onset of the death phase and led to an earlier _A. braunii_ death when compared to working at 2.5 mg/L of CBZ. Roughly, when the initial CBZ concentration was multiplied by a factor of four, the maximum concentration of algae was divided by the same factor. In addition, the growth profiles of the microalgae presented the same shape for both of the tested inoculum concentrations, but kinetics showed an interaction between CBZ and algae contents. Thus, when the initial inoculum concentration was multiplied by a factor of ten, the culture time necessary to reach the maximum algae concentration was divided approximately by a factor of two at constant initial CBZ concentration, whatever the considered initial pollutant concentration. In conclusion, the obtained data clearly showed that the presence of the target compound did not repress _A. braunii_ growth, despite its continuous exposure. For all tested conditions, the algae successfully grew in the presence of CBZ. This result is in agreement with previous studies that reported that the toxicity of organic compounds on cells could be attenuated by the uptake of non-toxic nutriments, such as the alternative carbon sources [39; 40; 41]. However, the initial CBZ concentration impaired the duration of the exponential phase of the growth phase, and the maximum cell number was reduced for all of the investigated conditions when the initial CBZ content was increased. Thus, the presence of the pollutant negatively affected the metabolic reactions associated with the algae's main metabolism (growth media BB or PP without CBZ). These trends corroborate the probable toxicity of CBZ on _A. braunii_, which increased with the initial xenobiotic concentration. Similar results were reported by [42] for the growth of _Staphylococcus xylosus_ in the presence of 2,4 dichlorophenol. In addition, the above results also indicate that an additional carbon source is needed to support cell growth in the presence of toxic compounds such as CBZ.