## 3 Results and Discussion
### Effect of Oxygen Mass Transfer Rate (KLA) on Culture Technological Effectiveness
In turn, the logarithmic growth stage brought about the most intense processes of lipid accumulation in cells and DHA synthesis (Figure 3c). Their final concentrations in the biomass reached 60.03 \(\pm\) 1.24 g/dm\({}^{3}\) and 25.32 \(\pm\) 0.56 g/dm\({}^{3}\), respectively (Figure 4, Table 4). In this variant, on average 442.0 g/dm\({}^{3}\) of glycerol were fed to bioreactors during the entire incubation cycle, resulting in its consumption yield at 3.68 g/dm\({}^{3}\).h, 3.28 g/gDCW (Table 4). The best, statistically comparable technological effects associated with DCW increase, lipid synthesis, and DHA accumulation in cells were observed in the culture variants 4 and 5 with k\({}_{\rm L}\)a values ranging from 600 1/h to 750 1/h. After 40 h of the adaptation phase, the DCW of _Schizochytrium_ sp. reached 37.37 \(\pm\) 3.14 g/dm\({}^{3}\) in variant 4 and 38.31 \(\pm\) 2.92 g/dm\({}^{3}\) in variant 5. After 120 h, the respective values reached 147.89 \(\pm\) 4.77 g/dm\({}^{3}\) (Figures 3d and 4, Table 4) and 149.03 \(\pm\) 3.31 g/dm\({}^{3}\) (Figures 3e and 4, Table 4). The final lipid concentration was determined at approximately 70.0 g/dm\({}^{3}\), whereas the final DHA concentration in biomass approximated 30.0 g/dm\({}^{3}\) (Figures 3d,e and 4, Table 4). Increasing the volumetric oxygen mass transfer rate and turbine speed in these variants contributed to the highest recorded values of r\({}_{\rm DHA}\) at 0.25 g/dm\({}^{3}\)-h and r\({}_{\rm DCW}\) at ca. 1.2 g/dm\({}^{3}\)-h (Table 4). Glycerol consumption yield in both these variants approximated 3.8 g/dm\({}^{3}\)-h and 3.2 g/gDCW (Table 4). In the study by [PERSON] et al. (2013) [67], increasing the value of k\({}_{\rm L}\)a coefficient from 143 \(\pm\) 19 1/h to 568 \(\pm\) 24 1/h and 1805 \(\pm\) 105 1/h resulted in DCW concentration exceeding 100 g/dm\({}^{3}\) \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Parameter** & **Unit** & **k\({}_{\rm L}\)a = 150** & **k\({}_{\rm L}\)a = 300** & **k\({}_{\rm L}\)a = 450** & **k\({}_{\rm L}\)a = 600** & **k\({}_{\rm L}\)a = 750** \\  & **[1/h]** & **[1/h]** & **[1/h]** & **[1/h]** & **[1/h]** & **[1/h]** \\ \hline Time [h] & [h] & 120 & 120 & 120 & 120 & 120 \\ DCW & [g/dm\({}^{3}\)] & 112.77 \(\pm\) 2.65 & 113.45 \(\pm\) 2.05 & 139.90 \(\pm\) 3.86 & 147.89 \(\pm\) 4.77 & 149.03 \(\pm\) 3.31 \\ Lipid & [g/dm\({}^{3}\)] & 48.90 \(\pm\) 1.56 & 49.34 \(\pm\) 1.25 & 60.03 \(\pm\) 1.24 & 69.44 \(\pm\) 0.76 & 69.88 \(\pm\) 0.81 \\ DHA & [g/dm\({}^{3}\)] & 21.02 \(\pm\) 0.73 & 22.15 \(\pm\) 0.65 & 25.32 \(\pm\) 0.56 & 29.44 \(\pm\) 0.36 & 30.05 \(\pm\) 0.71 \\ r\({}_{\rm DCW}\) & [g/dm\({}^{3}\).h] & 0.94 \(\pm\) 0.15 & 0.95 \(\pm\) 0.09 & 1.17 \(\pm\) 0.21 & 1.23 \(\pm\) 0.25 & 1.24 \(\pm\) 0.13 \\ r\({}_{\rm DHA}\) & [g/dm\({}^{3}\).h] & 0.18 \(\pm\) 0.08 & 0.18 \(\pm\) 0.05 & 0.21 \(\pm\) 0.02 & 0.25 \(\pm\) 0.15 & 0.25 \(\pm\) 0.09 \\ Glycerol & [g/dm\({}^{3}\).h] & 3.57 \(\pm\) 0.32 & 3.60 \(\pm\) 0.26 & 3.68 \(\pm\) 0.28 & 3.76 \(\pm\) 0.31 & 3.82 \(\pm\) 0.19 \\ consumption & [g/gDCW] & 3.97 \(\pm\) 0.76 & 3.99 \(\pm\) 0.64 & 3.28 \(\pm\) 0.59 & 3.16 \(\pm\) 0.22 & 3.18 \(\pm\) 0.15 \\ EPS & [g/dm\({}^{3}\)] & 8.73 \(\pm\) 0.09 & 8.62 \(\pm\) 0.12 & 8.94 \(\pm\) 0.06 & 9.17 \(\pm\) 0.23 & 9.08 \(\pm\) 0.17 \\ Viscosity & [mm\({}^{2}\)/s] & 20.97 \(\pm\) 0.74 & 21.03 \(\pm\) 1.02 & 21.33 \(\pm\) 0.68 & 21.07 \(\pm\) 0.91 & 21.43 \(\pm\) 1.13 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Parameters characterizing the effectiveness of _Schizochytrium_ sp. culture depending on k\({}_{\rm L}\)a value. Figure 4: Concentrations of DCW, DHA, and lipids depending on k\({}_{\rm L}\)a value. Those authors also showed that the value of k\({}_{\rm L}\)a coefficient affected assimilation of nutrients, microalgal biomass growth, and DHA synthesis. Literature data and the present study results enable the conclusion that higher k\({}_{\rm L}\)a values stimulate cell proliferation and lipid accumulation in microalgal biomass.