# Impact of 50 Hz Electromagnetic Field on the Growth of _Chlorella vulgaris_
## 3 Results and Discussions
The results of the comparative chemical analysis performed on the culture medium before inoculation \(c_{i}\) and after inoculation and 96 h of culture \(c_{f}\) (25 \(\pm\) 0.5 \({}^{\circ}\)C, continuous lighting with 300 \(\upmu\)mol/m\({}^{2}\)/s) are presented comparatively in Table 2.  
By analyzing the values in Table 2, it can be noticed that during the growth of _Chorella vulgaris_ Bienjerinck CCALA 269, a significant part of the nitrogen (N-NO\({}_{3}\)) and phosphorus content of the culture medium is retained/incorporated into the formed algal mass. Unlike the prokaryotes [40], green microalgae are unable to utilize atmospheric N\({}_{2}\) because it would require the usage of a consortium of nitrogen-fixing bacteria and  
Figure 5: The evolution of dissolved oxygen in the culture medium. microalgae to access such nitrogen species. As it is known, nitrogen serves as a crucial macronutrient that governs the metabolism, and consequently, the growth and biochemical composition of microalgae. As microalgae proliferate, they uptake nitrogen present in the growth medium to facilitate the biosynthesis of essential biological macromolecules like proteins, chlorophylls, and DNA [41]. The reproductive mechanism of the microalgae _C. vulgaris_ involves the production of asexual autospores through the division of the mother cell, resulting in 2-32 autospores, a process influenced by a range of environmental factors [36; 42]. The objective of the study was to investigate the impact of 50 Hz sinusoidal alternating electromagnetic field intensity on the growth of _C. vulgaris_ under non-limiting growth conditions, including temperature, nutrients, and light. The noticed enhancement in total nitrogen (TN\({}_{\text{b}}\)) levels in the culture subjected to varying field intensities could potentially be attributed to the stimulated influence of the electromagnetic field on the metabolic processes of _C. vulgaris_ (Table 2). It is interesting to note that TN\({}_{\text{b}}\) increases as algal mass increases. Thus, in the 96 h of growth in the case of the reference, an increase in TN\({}_{\text{b}}\) of only 8 mg/L was recorded, and in the case of growth stimulation by exposure to 50 Hz EMF, the nitrogen surplus increased significantly (21 mg/L at 2 V/m EMF, 57 mg/L at 5 V/m EMF, 96 mg/L at 10 V/m EMF, and 115 mg/L at 15 V/m EMF). These data indicate that, by exposing the culture medium mixed with air/CO\({}_{2}\) dispersed gas to 50 Hz EMF, the ability of _Chlorella vulgaris_ to metabolize nitrogen from culture media increases significantly (more than 14 times at 15 V/m EMF). In order to evaluate the depletion rate of P\({}_{\text{t}}\) nutrients and inorganic nitrogen N-NO\({}_{3}\) during the four days of growth, periodic comparative determinations were made (from 24 to 24 h). The recorded results are presented in Figure 6 (for nitrogen) and Figure 7 (for phosphorus). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multicolumn{6}{c}{**Concentrations [mg/L]**} \\ \cline{2-7}  & \(c_{i}\)\({}^{\star}\) & \(c_{f}\)**–reference \({}^{\star}\) (0 V/m)** & \(c_{f}\)**–2 V/m** & \(c_{f}\)**–5 V/m** & \(c_{f}\)**–10 V/m** & \(c_{f}\)**–15 V/m** \\ \hline N-NO\({}_{3}\) & 265 \(\pm\) 1.1 & 125 \(\pm\) 0.71 & 123 \(\pm\) 2.83 & 119 \(\pm\) 0.4 & 114 \(\pm\) 2.83 & 90 \(\pm\) 1.4 \\ TN\({}_{\text{b}}\) (total nitrogen) & 267 \(\pm\) 1.2 & 275 \(\pm\) 7.78 & 288 \(\pm\) 2.12 & 324 \(\pm\) 0.53 & 363 \(\pm\) 5.7 & 382 \(\pm\) 2.83 \\ Organic nitrogen (N\({}_{\text{alga}}\)) & 2 \(\pm\) 1.6 & 150 \(\pm\) 7.82 & 165 \(\pm\) 3.5 & 205 \(\pm\) 0.66 & 249 \(\pm\) 6.3 & 292 \(\pm\) 3.2 \\ P\({}_{\text{t}}\) (total phosphorus) & 14.5 \(\pm\) 0.1 & 0.91 \(\pm\) 0.003 & 0.87 \(\pm\) 0.1 & 0.7 \(\pm\) 0.001 & 0.68 \(\pm\) 0.008 & 0.65 \(\pm\) 0.003 \\ \hline \hline \end{tabular}  
* Average values for 3 determinations each; Mean \(\pm\) SD (N = 3), \(c_{f}\)–reference \({}^{\star}\)—final reference concentration (average value for 12 determinations); Mean \(\pm\) SD (N = 12).  
\end{table}