## 3 Results
### Impact of Tap Water Quality on Yeast Biomass Yield and Lipid Content
The carbon flux was evenly distributed between biomass and lipid synthesis in freshwater conditions. It is worth noting that the type of water used did not significantly affect the fatty acid profile [36]. The above results do not directly show the quality of tap water, but they confirm the adaptability of _Y. lipolytica_ yeast to various conditions. \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Test Parameter** & **Unit** & **Water C** & **Water P** & **Water B** & **Water U** & **Water Parameters and Acceptable** \\  & & & & & & **Variates** [35] \\ \hline pH (at 20 \({}^{\circ}\)C) & - & 7.0 \(\pm\) 0.2 & 8.1 \(\pm\) 0.2 & 7.0 \(\pm\) 0.2 & 7.7 \(\pm\) 0.2 & 6.5–9.5 \\ Electrical conductivity (Y25) & \(\mu\)S/cm & 3.0 \(\pm\) 1.0 & 1021.0 \(\pm\) 31.0 & 831.0 \(\pm\) 25.0 & 857.0 \(\pm\) 26.0 & 2500.0 \\ Nitrites (NO\({}_{2}\)) & mg/L & \(<\)0.033 & \(<\)0.033 & \(<\)0.033 & \(<\)0.033 & 0.50 \\  & & (0.033 \(\pm\) 0.005) & (0.033 \(\pm\) 0.005) & (0.033 \(\pm\) 0.005) & 0.50 \\ Nitrates (NO\({}_{3}\)) & mg/L & \(<\)0.1 & 5.41 \(\pm\) 0.76 & 5.31 \(\pm\) 0.75 & 0.71 \(\pm\) 0.10 & 50.0 \\ Ammonium ion & mg/L & \(<\)0.060 & \(<\)0.060 & \(<\)0.060 & \(<\)0.060 & 0.50 \\ (NH\({}_{4}\)) & mg/L & \((0.060\pm 0.013)\) & \((0.060\pm 0.013)\) & \((0.060\pm 0.013)\) & \((0.060\pm 0.013)\) & 0.50 \\ Hardness & mg/L & \(<\)1.0 & 252 \(\pm\) 38 & 230 \(\pm\) 35 & 400 \(\pm\) 60 & 60–500 \\ Chlorides & mg/L & \(<\)1.0 & 186 \(\pm\) 11 & 132 \(\pm\) 8 & 97 \(\pm\) 6 & 250.0 \\ Iron & \(\mu\)g/L & \(<\)5.0 & \(<\)5.0 & \(<\)5.0 & 18 \(\pm\) 2 & 200.0 \\ Manganese & \(\mu\)g/L & \(<\)0.1 & 1.4 \(\pm\) 0.1 & 2.6 \(\pm\) 0.3 & 10 \(\pm\) 1 & 50.0 \\ Oxidisability in & & & & & & \\ KMnO\({}_{4}\) & mg/L & \(<\)0.50 & \(<\)0.50 & \(<\)0.50 & \(<\)0.50 & 5.0 \\ (permanganate & & (0.50 \(\pm\) 0.08) & (0.50 \(\pm\) 0.08) & (0.50 \(\pm\) 0.08) & (0.50 \(\pm\) 0.08) & 5.0 \\ index) & & & & & & \\ Sulfates & mg/L & \(<\)5.0 & 65.2 \(\pm\) 9.8 & 72.7 \(\pm\) 11.0 & 162.0 \(\pm\) 25.0 & 250.0 \\ \hline \end{tabular}
\end{table} 
Table 1: Water analysis was used to prepare yeast culture media. Water C—control redistilled water, Water P—tap water collected at the left bank of the Vistula River in Warsaw (Praga-Poludnie District), Water B—tap water collected at the right bank of the Vistula River in Warsaw (Bielany District) and Water U—tap water collected at the right bank of the Vistula River in Warsaw (Ursynów District). In the second step, three batch or fed-batch cultures were conducted. This study evaluated the effects of water quality and culture time on yeast biomass yield, lipid biosynthesis, and biomass nutritional value. In addition, how the yeast growth phase affected the yield of microbial oil was investigated. Cultures were conducted for 20 or 65 h, with variants using untreated tap water or distilled water. Key parameters such as stirrer speed and medium oxygenation were monitored throughout the process (Figure 2a-c). In a 65 h culture with distilled water (Figure 2a), the cells entered a logarithmic growth phase after about 10 h, causing the oxygenation of the medium to drop to 50% of the initial value. As a result of intensive cell proliferation, there was a significant decrease in the oxygenation of the medium. Supplementation of the carbon source at 16, 50 and 62 h promoted lipid storage accumulation. Most of the waste oil depletion in medium occurred during the logarithmic growth phase, and each carbon source supplementation increased the stirrer speed, reflecting the higher oxygen demand as cell growth intensified. According to the knowledge of the biochemical pathways of microbial oil accumulation, a high carbon source-to-nitrogen ratio promotes lipid synthesis in oleaginous microbial cells [30]. The culture conducted in the tap water-based medium proceeded similarly to the medium prepared with distilled water for 65 h (Figure 2b). Waste oil was added at the 16 th hour of culture, during the logarithmic phase of yeast growth.