# Impact of 50 Hz Electromagnetic Field on the Growth of _Chlorella vulgaris_
## 3 Results and Discussions

Table 2: Chemical analysis results *. Figure 6: The comparative evolution of the N-NO\({}_{3}\) content of the culture medium. From the analysis of Figure 6, it is observed that after a first slow decrease during the lag period, the N-NO\({}_{3}\) concentration decreases linearly as the algal mass increases. The decrease is more accelerated (58 mg/L/day compared to 43 mg/L for the reference) under the influence of 15 V/m EMF when the algae growth rate is higher than the reference (Table 1). From the analysis of Figure 7, it is observed that after a first slow decrease during the LAG period, the P\({}_{\rm t}\) concentration drops sharply as the algal mass increases, and the decrease is more pronounced under the influence of 15 V/m EMF when the algae growth rate is higher than the reference (Table 1). It is also found that after approx. 48 h of growth by stimulation with 15 V/m ELF, 90% of the P\({}_{\rm t}\) reserve of the culture medium is depleted (compared to the reference, when 90% depletion is reached after approx. 80 h of growth). Comparing Figures 6 and 7 with Figure 4 leads to the conclusion that the limitations of the biomass growth rate in Figure 1 are due to the depletion in N-NO\({}_{3}\) and especially in P\({}_{\rm t}\) of the culture medium. It is noted that the presence of the phosphorus resource in the culture medium is determined in the biosynthesis of phospholipids that enter the structure of the cell membrane, the native rotary enzyme [18], and ATP [43], including chloroplast ATP [44], which together with the light harvesting complex have a determined role in the photosynthesis process (2) [45; 46; 47; 48]. Under these conditions, the rapid decrease in the phosphorus content of the culture medium for growth stimulated in 15 V/m EMF (Figure 7) can be explained by the increase in the growth rate of the algal mass following the stimulation of ATP synthesis. This is in good agreement with the results reported in [31] for _Escherichia coli_. By comparing the values from Table 1 (the concentration of biomass formed) with the values from Table 2, the nitrogen and phosphorus contents of the algal mass formed are calculated as:  
\[C_{Nitrogen}=100\cdot c_{\rm algal\ mass}/\rm N_{\rm algae}\ [\%] \tag{3}\]  
\[C_{\itphosphorus}=100\cdot c_{\rm algal\ mass}/(c_{\it P\rm t}-c_{\it P\rm t})\ [\%] \tag{4}\]  
The main source of nitrogen in the culture medium is NaNO\({}_{3}\) and that for phosphorus is K\({}_{2}\) HPO\({}_{4}\). Through the metabolism of nitrogen and phosphorus from these nutrients, the culture medium becomes alkaline. The comparative evolution of pH during the 96 h of growth at various intensities of the applied electric field is shown in Figure 8.  
Figure 7: The comparative evolution of the P\({}_{\rm t}\) content of the culture medium. The pH measurement during the 96 h of cultivation allowed the observation of the effect of 50 Hz EMF on the growth of C. vulgaris based on N-NO\({}_{3}\) and CO\({}_{2}\) consumption. The guidelines for preparing the BG11 medium included adjusting the pH to 7.1. Based on the data collected by the pH sensor, it was observed that following the commencement of aeration using a mixture consisting of 95% air and 5% CO\({}_{2}\) by volume, the pH values in each comparative experiment decreased from the initial range of 7.1-7.2 and stabilized within the range of 5.82-5.91. During the cultivation of _C. vulgaris_, the process of photosynthesis resulted in a gradual increase in the alkalinity of the culture medium and subsequent elevation of the pH. This phenomenon was consistently noted irrespective of the presence or absence of the electromagnetic field. However, under the influence of the 50 Hz EMF of 10 and 15 V/m, the pH evolution exhibited increased values in comparison to the reference. Figure 9 shows the nitrogen and phosphorus contents of the algal mass grown under reference conditions (EMF intensity = 0) and at various applied 50 Hz EMF intensities, calculated according to (3) and (4), respectively.