## 4 Conclusions
These results are confirmed from the optical microscopy images. For example, the Ni 5 and 10 ppm mono-MT cultures are degraded as no filaments--even broken--exist. Based on the findings from the pH measurements and FTIR analysis, an insight into the metal uptake mechanisms can be partially provided. Both pH measurements and FTIR analysis suggest that bioaccumulation is involved. More specifically, the lower increase in pH of the stressed cells than that in the Control ones testifies to their probable impaired photosynthetic capacity. In relation to the latter, the FTIR data confirmed changes in cellular composition and thus further confirmed bioaccumulation. However, metal adsorption on cell surfaces is a mechanism that cannot be discarded. \begin{table}
\begin{tabular}{c c c c c} \hline
\begin{tabular}{c} **Concentration** \\ **(ppm)** \\ \end{tabular} & **Metal Treatment** & **Day** & **Removal Efficiency Order** \\ \hline \multirow{4}{*}{1} & \multirow{4}{*}{Mono} & 3 & Zn \textgreater{} Pb \textgreater{} Cd \textgreater{} Cu \textgreater{} Ni \\ \cline{3-5}  & & 7 & Zn \textgreater{} Cd \textgreater{} Pb \textgreater{} Cu \textgreater{} Ni \\ \cline{2-5}  & & Multi & 3 & Cd \textgreater{} Cu \textgreater{} Pb \textgreater{} Zn \textgreater{} Ni \\ \cline{2-5}  & & 7 & Pb \textgreater{} Cd = Cu \textgreater{} Zn \textgreater{} Ni \\ \hline \multirow{4}{*}{5} & \multirow{4}{*}{Mono} & 3 & Pb \textgreater{} Zn \textgreater{} Cd \textgreater{} Ni \textgreater{} Cu \\ \cline{2-5}  & & 7 & Pb \textgreater{} Zn \textgreater{} Cd \textgreater{} Ni \textgreater{} Cu \\ \cline{2-5}  & & Multi & 3 & Cd \textgreater{} Pb \textgreater{} Zn \textgreater{} Cu \textgreater{} Ni \\ \cline{2-5}  & & 7 & Cd = Pb \textgreater{} Zn \textgreater{} Cu \textgreater{} Ni \\ \hline \multirow{4}{*}{10} & \multirow{4}{*}{Mono} & 3 & Pb \textgreater{} Zn \textgreater{} Cd \textgreater{} Ni \textgreater{} Cu \\ \cline{2-5}  & & 7 & Zn \textgreater{} Pb \textgreater{} Cd \textgreater{} Ni \textgreater{} Cu \\ \cline{2-5}  & & Multi & 3 & Zn \textgreater{} Pb \textgreater{} Cd \textgreater{} Ni \textgreater{} Cu \\ \cline{2-5}  & & 7 & Zn \textgreater{} Pb \textgreater{} Cd \textgreater{} Cu \textgreater{} Ni \\ \hline \end{tabular}
\end{table} 
Table 2: Removal efficiency order per metal for mono- and multi-MT cultures. Finally, based on the quality of the biomass after metal treatment, it is evident that it could be used for energy production using their saccharide content [13; 63], and their polyunsaturated fatty acid content [13; 63], for the production of biofuels, while the _A. platensis_ polysaccharide content was reported for its use in bio-stimulants, as in material synthesis [71]. Biomasses used as a bio-adsorbent can be repurposed for sustainable applications in alignment with circular economy principles. Spent biomasses enriched with metals can be transformed into value-added products like catalysts, soil enhancers, and capacitors, or used for energy production in fuel cells or biochar synthesis, retaining adsorptive properties [33]. Based on the above, _A. platensis_ appears to be a great candidate for the simultaneous bioremediation of heavy metal-contaminated waters, showing high growth rates and high removal efficiency for most metals. At the same time, the contaminated biomass has a high content in high-value substances that could be extracted and further used in various applications, supporting a green decontamination approach in the frame of circular economy. Conceptualization, N.A.K. ; methodology, L.M., E.K., N.K., E.N., and N.A.K. ; software, N.A.K. ; validation, L.M., E.K., N.K., and N.A.K. ; formal analysis, L.M., E.K., and N.K. ; investigation, L.M., E.K., N.K., E.N., and N.A.K. ; resources, N.A.K. ; data curation, L.M., E.K., and N.K. ; writing--original draft preparation, L.M., E.K., and N.K. ; writing--review and editing, L.M., E.K., N.K., and N.A.K. ; visualization, L.M. ; supervision, N.A.K. ; project administration, N.A.K. ; funding acquisition, N.A.K.