## 3 Results and Discussion
### Effect of Oxygen Mass Transfer Rate (KLA) on Culture Technological Effectiveness  
The method of oxygen supply determines its solubility in the culture medium in aerobic biotechnological processes [44; 63]. Investigations conducted thus far have shown that providing the appropriate oxygen supply to the culture significantly increases the growth of _Schizochytrium_ sp. cells and DHA synthesis in the biomass [35; 62; 64]. Oxygen transfer to cells has been found to be strongly affected by culture medium viscosity, whose increase observed in microbiological cultures is due to EPS synthesis [65]. The increased viscosity of the culture medium diminishes the effectiveness of oxygen transfer to cells, which affects the effectiveness of waste glycerol consumption and its conversion to DHA. Hence, it is essential to search for a method of air supply to the system that would be justified by both final technological effects and operating costs. Regardless of the applied kLA coefficient value, each culture entered into three growth phases: adaptation phase (1) spanning from 0 to 40 th hour, logarithmic growth phase (2) observed between the 40 th hour and 80 th-100 th hour, and stationary growth phase (3) observed since the 80 th-100 th hour to 120 th hour of incubation. In the variant with kLA = 150 1/h, biomass DCW increased from 5.0 \(\pm\) 1.0 g/dm\({}^{3}\) to 22.42 \(\pm\) 1.09 g/dm\({}^{3}\) in phase 1, from 22.42 \(\pm\) 1.09 g/dm\({}^{3}\) to 87.60 \(\pm\) 2.79 g/dm\({}^{3}\) in phase 2, and reached the final value of 112.77 \(\pm\) 2.65 g/dm\({}^{3}\) in phase 3 (Figures 3a and 4, Table 4). The concentrations of lipids and DHA peaked in the logarithmic growth stage to reach the final values of 48.90 \(\pm\) 1.56 g/dm\({}^{3}\) and 21.02 \(\pm\) 0.73 g/dm\({}^{3}\), respectively (Figure 4). Similar values of biomass production, lipid accumulation, and DHA synthesis were obtained in variant 2 with kLA = 300 1/h (Figures 3b and 4, Table 4). Glycerol consumption yield in both these variants approximated 3.6 g/dm\({}^{3}\cdot\)h and 4.0 g/gDCW (Table 4). [PERSON] et al. (2010) [35] confirmed in their study that kLA = 150 1/h promoted cell growth within the first 40 h of incubation and that decreasing the value of this coefficient to 88.5 1/h increased final DHA concentration in cells. The above observations were presumably due to the microalgae capability for lipid accumulation under conditions of substrate stress [66]. In the culture of _Schizochytrium_ sp. described by [PERSON] et al. (2013) [67], the use of kLA = 143 \(\pm\) 19 1/h ensured biomass DCW concentration at 25.56 \(\pm\) 1.60 g/dm\({}^{3}\) and DHA concentration at barely 2.28 g/dm\({}^{3}\). The low values of the above parameters can be explained by poor availability of oxygen molecules to microalgal cells and, consequently, by the impaired metabolic activity in the cycle of tricarboxylic acid or/and lipogenesis. \begin{table}
\begin{tabular}{c c} \hline \hline
**Saccharide Monomer** & **Molar Percentage [\% mol]** \\ \hline Glucose & 60.64 \(\pm\) 1.93 \\ Galactose & 18.00 \(\pm\) 1.13 \\ Mannose & 11.47 \(\pm\) 0.71 \\ Fucose & 7.23 \(\pm\) 0.62 \\ Xylose & 2.66 \(\pm\) 1.28 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Composition of saccharide monomers of the EPS polysaccharide fraction. Figure 3: Changes in concentrations of _Schizophrenia_ sp. DCW, lipids, and DHA in the biomass at k\({}_{\rm{L}}\)a values of: (**a**) 150 [1/h], (**b**) 300 [1/h], (**c**) 450 [1/h], (**d**) 600 [1/h], and (**e**) 750 [1/h]. In the culture variant with k\({}_{\rm L}\)a = 450 1/h, DCW of microalgae increased from 5.0 \(\pm\) 1.0 g/dm\({}^{3}\) to 35.63 \(\pm\) 3.83 g/dm\({}^{3}\) in the adaptation phase, while at the end of phase 2 (after 100 h of incubation) it reached 130.46 \(\pm\) 4.53 g/dm\({}^{3}\). The stationary growth phase yielded the DCW concentration of 139.90 \(\pm\) 3.86 g/dm\({}^{3}\) at the end of the incubation cycle (Figures 3c and 4, Table 4).