## 4 Conclusions  
This work shows, for the first time, that wood enzymatic hydrolysate containing glucose can be used as a feedstock to produce _Chlorella_ biomass, fatty acids and pigments in the dark. In the literature, high microalgal cell densities can be achieved during heterotrophic cultivation in scaled-up bioreactors [28]. Hence, application of this wood hydrolysate to microalgae cultivation in the dark could be interesting in terms of industrial production in large-volume closed tanks [25]. However, the \begin{table}
\begin{tabular}{c c c c} \hline
**Fatty Acid Production** & **TGP (36 h)** & **TGP-Enz10 (42 h)** & **TGP-Cit10 (52 h)** \\ \hline Biomass productivity (mg L\({}^{-1}\) d\({}^{-1}\))\({}^{\text{A}}\) & 403 \(\pm\) 20 & 345 \(\pm\) 20 & 279 \(\pm\) 15 \\ Total fatty acid content (\% d.w.) & 3.6 \(\pm\) 0.05 & 3.5 \(\pm\) 0.1 & 3.7 \(\pm\) 0.1 \\ Fatty acid productivity (mg L\({}^{-1}\) d\({}^{-1}\)) & 14.5 \(\pm\) 0.72 & 12.1 \(\pm\) 0.6 & 10.32 \(\pm\) 0.52 \\ \hline \multicolumn{4}{c}{Fatty acid (FA) composition (\% of total fatty acids)} \\ \hline C14:0 & 1.00 \(\pm\) 0.1 & 1.27 \(\pm\) 0.1 & 1.26 \(\pm\) 0.23 \\ C16:0 & 29 \(\pm\) 1.5 & 29.15 \(\pm\) 0.63 & 28.3 \(\pm\) 0.56 \\ C18:1 & 5.85 \(\pm\) 0.5 & 8.31 \(\pm\) 0.56 & 8.75 \(\pm\) 0.78 \\ C18:2 & 26.1 \(\pm\) 0.5 & 41.28 \(\pm\) 0.39 & 45.33 \(\pm\) 0.52 \\ C18:3 & 38.4 \(\pm\) 1.2 & 19.85 \(\pm\) 1.62 & 16.25 \(\pm\) 0.49 \\ \hline \multicolumn{4}{c}{\({}^{\text{A}}\) Average daily biomass productivity after specific cultivation time (24+ h). d.w. means dry weight.} \\ \end{tabular}
\end{table} 
Table 1: Biomass productivity, total fatty acid (FA) content, fatty acid productivity and fatty acid composition in _Chlorella_ cultures cultivated on 1 g/L glucose (TGP), wood enzymatic 10% hydrolysate containing 1 g/L glucose (TGP-Enz10), and 1 g/L glucose supplemented with 10% neutralized citrate buffer loading (TGP-Cit10). Cultivation conditions: photobioreactor under heterotrophic mode (0 \(\mu\)E m\({}^{-2}\) s\({}^{-1}\)) at 25 \({}^{\circ}\)C. Number of independent experiments: 3. \begin{table}
\begin{tabular}{c c c c} \hline
**Pigment Production** & **TGP (36 h)** & **TGP-Enz10 (42 h)** & **TGP-Cit10 (52 h)** \\ \hline Biomass productivity (mg L\({}^{-1}\) d\({}^{-1}\))\({}^{\text{A}}\) & 403 \(\pm\) 20 & 345 \(\pm\) 20 & 279 \(\pm\) 15 \\ Chl\({}_{\text{Total}}\) content (\% d.w.) & 1.215 \(\pm\) 0.065 & 1.24 \(\pm\) 0.03 & 1.288 \(\pm\) 0.108 \\ Chl\({}_{\text{Total}}\) productivity (mg L\({}^{-1}\) d\({}^{-1}\)) & 4.89 \(\pm\) 0.25 & 4.278 \(\pm\) 0.21 & 3.59 \(\pm\) 0.18 \\ Chl\({}_{\text{$a/b$ ratio (-)}}\) & 3.67 \(\pm\) 0.09 & 3.645 \(\pm\) 0.085 & 3.857 \(\pm\) 0.337 \\ Car\({}_{\text{Total}}\) content (\% d.w.) & 0.297 \(\pm\) 0.016 & 0.313 \(\pm\) 0.008 & 0.337 \(\pm\) 0.03 \\ Car\({}_{\text{Total}}\) productivity (mg L\({}^{-1}\) d\({}^{-1}\)) & 1.19 \(\pm\) 0.06 & 1.08 \(\pm\) 0.054 & 0.94 \(\pm\) 0.047 \\ Chl\({}_{\text{Total}}\)/Car\({}_{\text{Total}}\) ratio (-) & 4.09 \(\pm\) 0.05 & 3.96 \(\pm\) 0.11 & 3.82 \(\pm\) 0.18 \\ \hline \multicolumn{4}{c}{\({}^{\text{A}}\) Average daily biomass productivity after specific cultivation time (24+ h). d.w. means dry weight.} \\ \end{tabular}
\end{table} 
Table 2: Chlorophyll (Ch\({}_{\text{Total}}\)) content, carotenoid (Car\({}_{\text{Total}}\)) content and pigment productivity in _Chlorella_ cultures cultivated on 1 g/L glucose (TGP), wood enzymatic 10% hydrolysate containing 1 g/L glucose (TGP-Enz10), and 1 g/L glucose supplemented with 10% neutralized citrate buffer loading (TGP-Cit10). Cultivation conditions: photobioreactor under heterotrophic mode (0 \(\mu\)E m\({}^{-2}\) s\({}^{-1}\)) at 25 \({}^{\circ}\)C. Number of independent experiments: 3.  
hydrolysate used in this study was shown to suppress _Chlorella_ growth during heterotrophic cultivation, when compared to synthetic TGP medium. A constituent of wood hydrolysate that possesses inhibitory activity was found to be a neutralized citrate buffer.