# Microalgal Growth in Aquaculture Effluent: Coupling Biomass Valorisation with Nutrients Removal
## 3 Results and Discussion
### Biomass Valorisation
\begin{table}
\begin{tabular}{c c c} \hline \multicolumn{1}{c}{**Parameters**} & **AW** & **C+** \\ \hline Carbohydrates (\% \(w/w\)) & 48.64 \(\pm\) 0.83 \({}^{\text{a}}\) & 34.10 \(\pm\) 1.74 \({}^{\text{b}}\) \\ Proteins (\% \(w/w\)) & 17.93 \(\pm\) 1.21 \({}^{\text{a}}\) & 20.98 \(\pm\) 0.34 \({}^{\text{a}}\) \\ Lipids (\% \(w/w\)) & 15.82 \(\pm\) 0.15 \({}^{\text{a}}\) & 14.98 \(\pm\) 0.17 \({}^{\text{b}}\) \\ Chlorophyll a (\% \(w/w\)) & 0.68 \(\pm\) 0.02 \({}^{\text{a}}\) & 1.58 \(\pm\) 0.02 \({}^{\text{b}}\) \\ Chlorophyll b (\% \(w/w\)) & 0.33 \(\pm\) 0.01 \({}^{\text{a}}\) & 0.69 \(\pm\) 0.01 \({}^{\text{b}}\) \\ Chlorophyll a + b (\% \(w/w\)) & 0.99 \(\pm\) 0.04 \({}^{\text{a}}\) & 2.28 \(\pm\) 0.03 \({}^{\text{b}}\) \\ Carotenoids (\% \(w/w\)) & 0.21 \(\pm\) 0.01 \({}^{\text{a}}\) & 0.37 \(\pm\) 0.01 \({}^{\text{b}}\) \\ \hline \end{tabular}
\end{table} 
Table 5: Biochemical composition of the biomass in terms of carbohydrates, proteins, lipids, and photosynthetic pigments. aquaculture wastewater and achieved 37.1% of carbohydrate content and protein content of 24.9%. Additionally, [PERSON] et al. [13] obtained a carbohydrate content of 29.8 \(\pm\) 0.1%, protein content of 39.5 \(\pm\) 0.2% and lipid content of 16.1 \(\pm\) 0.1% after 5 d of cultivation in real aquaculture wastewater of _C. vulgaris._  
In this study, besides treating aquaculture wastewater, the goal was also to valorise the biomass obtained in the AW assay by analysing the biochemical composition of the produced biomass. One way to valorise microalgal biomass is to integrate it into aquaculture feed. Microalgae have probiotic properties in fish and other properties, such as immunostimulants, antiviral and antibacterial, that impact survival and growth rates, as well as the immune system of fish and other aquatic organisms [22]. However, for the time being, microalgae are more effective as a supplement to existing feed than as a total replacement for feed. Several articles in this area show results that favour supplementary use instead of total use. [PERSON] et al. [40] incorporated 5 to 10% of _Dunaliella salina_ in a giant tiger prawn aquaculture and obtained an increase in the survival rate due to an improvement in the immune system and an increase in the antioxidant content. The same occurred with [PERSON] et al. [41], who, by incorporating 6 to 8% of _C. vulgaris_ in the feed of a giant tiger prawn aquaculture, observed an increase in the growth rate and a better immune response. In addition, the tested prawns gained resistance to _Aeromonas hydrophila_ infection. On the other hand, [PERSON] et al. [42] completely replaced the nutritional diet with microalgae _Schizochytrium_ sp. and did not observe significant differences in survival rate. Identically, [PERSON] et al. [43] incorporated the microalgae _Pavlova viridis_ and _Nannochloropsis_ sp. between 50 and 100% and observed no adverse consequences on growth or nutrient intake, but neither did they reported any advantages. The analysis of the microalgal biomass compounds is important because each one influences the metabolism and organism of fish and other aquatic species differently. Carbohydrates are easily digestible depending on their type and the amount present in the biomass, as well as the species of the aquatic organisms used [22]. A study on Nile Tilapia revealed that microalgae _C. vulgaris_ and _Spirulina maxima_ present good carbohydrate digestibility, with _C. vulgaris_ being the one that is more easily digested [44]. On the other hand, microalgae proteins are a great alternative to the current proteins present in the commercial feed, regarding the amino acid composition. Furthermore, microalgal lipids have a lower degree of contamination than those present in the typical fish oil used in aquaculture [22]. Finally, vibrant colour pigments, such as carotenoids, are widely used because of their ability to enhance the quality and nutritional value of some aquatic organisms.