## 3 Results and Discussion
### Waste-Derived VFA for DHA and OCFA Production in Fed-Batch Fermentations  
Biomass Production and VFA Consumption Pattern  
Since the capacity of _Schizochytrium limacinum_ to grow on both single and VFA mixtures was verified in batch culture and bioreactor, the purpose of this study was to evaluate the cultivation of this microalgae on VFA from an industrial effluent with the composition  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Carbon** & **DCW** & **Biomass Productivity** & **Biomass Yield** & **Lipids (\%)** & **DHA** & **C15:0** & **C17:0** \\
**Source** & **(g/L)** & **(g/L)** & **(g-g\({}^{-1}\) Substrate)** & **(\%/TFA)** & **(\%/TFA)** & **(\%/TFA)** \\ \hline Synthetic VFA & 12.3 \(\pm\) 0.1 & 0.23 \(\pm\) 0.1 & 1.23 \(\pm\) 0.01 & 45.9 \(\pm\) 1.0 & 18.3 \(\pm\) 0.9 & 14.3 \(\pm\) 0.7 & 4.9 \(\pm\) 0.6 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Synthetic VFA 2L bioreactor.  
Figure 3: Distribution of fatty acids on acetic, propionic, butyric, valeric and synthetic VFA mixture experiments.  
defined in point 2.3. The capacity of waste derived VFAs as a carbon source resulted in a lipid accumulation of 54% _w/w_, 18.5 DCW/L of biomass, and a fatty acid profile containing 51.6% saturated fatty acids and 47.9% polyunsaturated fatty acids. OCFA are presented in 25.0% of TFA, comprising C15:0 and C17:0 at 18.1 and 6.9%, respectively. DHA as the main fatty acid compound found in _Schizochytrium limacinum_ resulted in almost 50% of TFA and 46.3% of TFA (Table 3).  
The analysis of VFA throughout the experiment showed that during the first 24 h of cultivation, over 75% of the carbon source was consumed, and it was practically exhausted at 53 h where 93.2% VFA was already consumed by microalgae (Figure 4). However, as it was described in Section 3.1., VFAs were not consumed in the same way. Acetic and butyric acid were consumed faster than odd-chain VFA, propionic and valeric acid. Meanwhile, most of them were consumed at 49 h of the growth experiment, while propionic acid exhibited 23.9% of its initial content at this time in the experiment (Figure 5).  
Figure 4: Biomass production vs. waste-derived VFA consumption.  
Figure 5: Evolution of each VFA during fermentation.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Carbon Source** & **DCW** & **Biomass Productivity** & **Biomass Yield** & **Lipids** & **DHA** & **C150** & **C170** \\  & **(g/L)** & **(g/L)** & **(g g\({}^{-1}\) Substrate)** & **(\%)** & **(\%)** & **(\% TFA)** & **(\% TFA)** \\ \hline Waste-derived VFA & \(18.5\pm 0.1\) & \(0.35\pm 0.1\) & \(1.85\pm 0.01\) & \(54.0\pm 1.2\) & \(46.3\pm 0.8\) & \(18.1\pm 0.7\) & \(6.9\pm 0.7\) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Waste derived VFA 2L bioreactor.  
In this study, the effect of carbon source consumption on the fatty acid profile was also evaluated. As shown in Figure 6, when the carbon source associated with butyric and valeric acid was consumed, and propionic and valeric acid were still in the media, _Schizochytrium limacinum_ used these short fatty acids as a carbon source and, consequently, the fatty acid profile showed higher content in OCFA, C15:0 and C17:0.  
The parameters related to the two types of cultivation are summarized in Table 4.