# Microalgal Growth in Aquaculture Effluent: Coupling Biomass Valorisation with Nutrients Removal
## 3 Results and Discussion
### Biomass Valorisation  
The biochemical composition of the produced biomass was evaluated, and the contents of the analysed compounds are summarised in Table 5.  
As can be observed from Table 5, the obtained carbohydrate content was statistically higher (\(p\) < 0.05) in the AW assay (48.64 \(\pm\) 0.83%), compared to the C+ assay (34.10 \(\pm\) 1.74%). These values are higher than the typical range of carbohydrate content for _C. vulgaris_, 12 to 17% [37]. The protein content obtained in the C+ assay (20.98 \(\pm\) 0.34%) and AW (17.93 \(\pm\) 1.21%) were not statistically different (\(p\) > 0.05). These values are lower than the ones mentioned in the literature (40 and 60%) [38]. This happened possibly due to a stress response to the nutrient depletion that occurs in the final growth stage (see Figure 3). During stress conditions, the protein content in microalgae decreases [39]. It was also possible to note that the lipid content obtained in AW (15.82 \(\pm\) 0.15%) was statistically higher (\(p\) < 0.05) than in C+ (14.98 \(\pm\) 0.17%) and that both values were similar to the values referenced in the literature (14-22%) [37]. Lastly, in the positive control, there was a higher production of pigments, with chlorophyll a representing the highest content (1.58 \(\pm\) 0.02%) and carotenoids the lowest (0.37 \(\pm\) 0.01%). This behaviour was also observed in the AW trials: the pigment produced the most was chlorophyll a (0.68 \(\pm\) 0.02%), and the least produced was carotenoids (0.21 \(\pm\) 0.01%). [PERSON] et al. [36] grew _C. sorokiniana_ in \begin{table}
\begin{tabular}{c c c c} \hline \multirow{2}{*}{**Assay**} & \multicolumn{2}{c}{**Y\({}_{\text{X/S}}\) (g\({}_{\text{dw}}\) g\({}_{\text{s}}\)\({}^{-1}\))**} \\ \cline{2-4}  & **TN** & **NO\({}_{\text{3}}\)-N** & **PO\({}_{\text{4}}\)-P** \\ \hline AW & 19.0 \(\pm\) 1.4 \({}^{\text{a}}\) & 21.9 \(\pm\) 1.1 \({}^{\text{a}}\) & 62.7 \(\pm\) 3.2 \({}^{\text{a}}\) \\ C+ & 10.9 \(\pm\) 0.3 \({}^{\text{b}}\) & 10.0 \(\pm\) 0.1 \({}^{\text{b}}\) & 38.9 \(\pm\) 0.1 \({}^{\text{b}}\) \\ \hline \end{tabular} \(\text{Y}_{\text{X/S}}\)—biomass yield coefficient. In the same column, the values with a common letter (\({}^{\text{a}}\) and \({}^{\text{b}}\)) are not statistically different (\(p\) > 0.05).  
\end{table} 
Table 4: Biomass yield coefficient regarding total nitrogen, nitrate-nitrogen and phosphate-phosphorus. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \multirow{2}{*}{**Nutrient**} & \multirow{2}{*}{**Assay**} & **S\({}_{\text{0}}\)** & **RE** & \(\lambda\) & **k** & **RMSE** \\  & & **(mg L \({}^{-1}\))** & **(\%)** & **(d)** & **(d\({}^{-1}\))** & **R\({}^{2}\)** & **(mg L \({}^{-1}\))** \\ \hline TN & AW & 20.2 \(\pm\) 0.5 \({}^{\text{a}}\) & 93.5 \(\pm\) 2.1 \({}^{\text{a}}\) & 0.38 \(\pm\) 0.66 & 0.83 \(\pm\) 0.26 & 0.994 & 0.797 \\  & C+ & 43.5 \(\pm\) 0.5 \({}^{\text{b}}\) & 95.6 \(\pm\) 1.4 \({}^{\text{a}}\) & 1.66 \(\pm\) 0.42 & 0.44 \(\pm\) 0.07 & 0.998 & 1.243 \\ NO\({}_{\text{3}}\)-N & AW & 10.7 \(\pm\) 0.8 \({}^{\text{a}}\) & 98.0 \(\pm\) 0.1 \({}^{\text{a}}\) & 0.67 \(\pm\) 0.39 & 0.92 \(\pm\) 0.21 & 0.998 & 0.281 \\  & C+ & 38.0 \(\pm\) 0.3 \({}^{\text{b}}\) & 99.4 \(\pm\) 0.1 \({}^{\text{b}}\) & 0.00 \(\pm\) 1.46 & 0.48 \(\pm\) 0.18 & 0.994 & 1.926 \\ PO\({}_{\text{4}}\)-P & AW & 2.2 \(\pm\) 0.1 \({}^{\text{a}}\) & 92.7 \(\pm\) 0.1 \({}^{\text{a}}\) & 0.45 \(\pm\) 0.11 & 1.48 \(\pm\) 0.16 & 1.000 & 0.013 \\ C+ & 10.4 \(\pm\) 0.1 \({}^{\text{b}}\) & 98.4 \(\pm\) 0.1 \({}^{\text{b}}\) & 1.63 \(\pm\) 0.45 & 0.49 \(\pm\) 0.09 & 0.998 & 0.313 \\ \hline \end{tabular}
\end{table} 
Table 3: Removal efficiencies, modified Gompertz model parameters and fitting performance indexes achieved for each assay.