## 4 Conclusions  
An original biological treatment for the removal of carbamazepine (CBZ), a highly persistent molecule in wastewater treatment plants, was investigated in this work using the algae _Ankistradesmus braunii_ (_A. braunii_). Experimental data demonstrated first that CBZ is efficiently removed; up to 87.6% CBZ was found to be eliminated at high _A. braunii_ concentrations of \(10^{5}\) cells/mL, starting with an initial  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Metabolite** & **Experimental m/z** \\ \hline
1: 10-hydroxycardbamazepine & & \\
10-OH CBZ & & \\
2: 4-carboxy-10-carboxamido- & & \\
9(10H)-cridone & & \\
3: 10-hydroxy-11-oxa- & & \\ carbamazepine & & \\ \hline \hline \end{tabular}
\end{table}
Table 4: CBZ metabolites detected by ultraperformance liquid chromatography-tandem mass spectrometry (UHPLC/MS/MS).  
Figure 7: Proposed oxidation reaction of CBZ by _A. braunii_ and the formation of 10-OH CBZ.  
CBZ concentration of 2.5 mg/L. The removal of CBZ was enhanced by increasing the concentration of algae and impaired by initial higher concentrations of CBZ after 60 days. On the contrary, from a kinetic point of view, high CBZ contents and lower inoculum concentrations promoted a more rapid elimination of CBZ, despite the lower final values of the removal yield. This highlights the dual role of CBZ that is a nutritive source for the algae but seems to be toxic at a high dose. An analysis of the fate of CBZ confirmed that about 80% of the CBZ removed was accumulated in _A. braunii_ cells, but the presence of several metabolites found in the cell-free supernatant and in the cells indicated that biotransformation of CBZ also occurred in parallel: three main metabolites of CBZ have been identified, and the surface area of secondary peaks in HPLC chromatograms was clearly negatively correlated with the peak of CBZ.  
Finally, all these results prove that a biological treatment using _A. braunii_ could be more efficient for the removal CBZ from water than many other conventional techniques, either biological or physicochemical. However, treatment time remained long, and its effectiveness depends on other carbon sources. So, further work is still needed to circumvent these drawbacks, first to optimize the parameters of the _A. braunii_ growth, and then to investigate the ability of _A. braunii_ to remove CBZ in real water in relation to the influence of the culture media used in this work.  
Conceptualization, C.V., T.Y., G.E.B., F.A., and L.F.; formal analysis, N.F., H.B., and L.F.; investigation, T.Y., N.F., and L.F.; methodology, T.Y., H.B., G.E.B., and C.V.; resources, F.A., and L.F.; software, N.F., and F.A.; supervision, C.V., F.A., G.E.B., and L.F.; validation, T.Y., N.F., H.B., F.A., G.E.B., C.V., and L.F.; Writing--Original draft, T.Y., C.V., and L.F. All authors have read and agreed to the published version of the manuscript.  
Part of this work was supported by the project \"Excellence, performance and competitiveness in the Research, Development and Innovation activities\" at \"Dunarea de Jose University of Galati\", acronym \"EXPERT\", financed by the Romanian Ministry of Research and Innovation in the framework of Programme 1--Development of the national research and development system, Sub-programme 1.2--Institutional Performance--Projects for financing excellence in Research, Development and Innovation, Contract No. 14 PFE/17.10.2018.  
[PERSON] and C.V. are thankful to the Chemical and Process Engineering laboratory for the analytical support in the identification of the biodegradation metabolites. The authors declare no conflict of interest.