## 3 Results
### Outdoor Setup  
The microalgae in the outdoor setup did aggregate and settle like the indoor setup, but the culture stayed homogeneous for a few hours after manual mixing, with only a few larger aggregates that settled rapidly. Before manual resuspension, the supernatant appeared clear (OD\({}_{750}\) = 0.03), while the culture remained opaque for a few hours after mixing (OD\({}_{750}\) \(\approx\) 0.30 every experimental day). As shown in Figure 8, chlorophyll autofluorescence changed, resulting in dimmer cells. Alcian Blue staining showed the presence of acidic mucopolsaccharide in the aggregates (Figure 8f). TEM observation showed the presence of bacteria and cell wall remnants in the culture medium. Both TEM observation (Figure 9b) and NR staining (Figure 8e) showed the presence of lipid droplets in some cells. Figure 8: Light and fluorescence microscopy view of microalgae grown in the outdoor setup at 0 (**a,b**) and 14 (**c,d**) days of cultivation. Autofluorescence after 14 days decreased, resulting in dimmer cells. In (**e**) the presence of lipid droplets (arrow) inside the cells is highlighted thanks to Nile Red staining. In (**f**), the presence of acidic mucopolsaccharides on the 14 th day is highlighted thanks to Alcian Blue staining. Bars, 5 \(\upmu\)m. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Unit** & **Day 0** & **Day 20** \\ \hline COD & O\({}_{2}\) mg L\({}^{-1}\) & 64 & 38 \\ BOD\({}_{5}\) & O\({}_{2}\) mg L\({}^{-1}\) & 15 & \textless{}10 \\ Total suspended solids & mg L\({}^{-1}\) & 38 & 8 \\ _Escherichia coli_ & CFU/100 mL & 48,880 & \textless{}2 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Estimated media composition after the inoculum in the indoor experiment, calculated considering dilution, and media composition at the end of the indoor experiment. At the end of cultivation, the media was collected before the manual resuspension, and it was not centrifuged. The concentration of dry biomass at the end of the experiment (0.099 g\({}_{\text{DW}}\) L\({}^{-1}\)) was not significantly different from the initial one (0.090 g\({}_{\text{DW}}\) L\({}^{-1}\)), but some fluctuations were recorded. In particular, the concentrations recorded on day 3 (0.100 g\({}_{\text{DW}}\) L\({}^{-1}\)) and day 17 (0.102 g\({}_{\text{DW}}\) L\({}^{-1}\)) were significantly higher than the initial value (Figure 10). For a report of the ANOVA analysis, see Table S2 in the Supplementary Materials. The concentration of photosynthetic pigments dropped since day 3. Two other significant decreases were recorded in Chl \(a\) and Car concentrations on days 14 and 17 compared with the concentrations recorded on the previous days (Figure 11a,c). The variations in pigment concentrations affected both the Chl _a_/Chl \(b\) and Chl/Car ratio, with a significant increase in the Chl _a_/Chl \(b\) ratio since day 14 and a significant drop in the Chl/Car ratio since day 17 (Figure 11d,e). The PSII maximum quantum yield decreased since the first day, reaching its lowest value on days 10-14. Interestingly, after these days the F\({}_{\text{V}}\)/F\({}_{\text{M}}\) value increased with significant changes every day (Figure 11f). For a report of the ANOVA analyses, see Table S2 in the Supplementary Materials. Figure 10: Microalgal biomass yield expressed as grams of algal dry weight per liter of the culture grown outdoors. Data refers to means \(\pm\) standard deviations (n = 3). Different letters highlight significant differences between groups (\(p\leq\) 0.05) found using a one-way ANOVA. Figure 9: Transmission electron microscopy images of the microalgae grown outdoors on the 20 th day. In (**a**) a cell with lipid droplets (L) and cell wall remnants (R) in the media are visible. In (**b**) two cells with a thick outer wall (W) are visible. In both images, other organisms (B) are visible in the medium.