# Impact of 50 Hz Electromagnetic Field on the Growth of _Chlorella vulgaris_
## 3 Results and Discussions  
The results of the respective spectrophotometric determinations, and the comparative absorbance evolution of the algal mass suspension in the liquid culture medium taken from the reference photobioreactor and from that exposed to growth stimulation by EMF of 2, 5, and 10, at 15 V/m, in the first 96 h after inoculation, are synthetically presented in Figure 3. Its analysis shows that at the beginning, in the first hours after inoculation, the absorbance did not change significantly during the lag period [39] (in the reference photobioreactor it lasted approximately 8 h) and was reduced as the 50 Hz EMF intensity increased, to approximately 6 h for EMF 2 V/m, 4.5 h for EMF 5 V/m, 3.2 h for EMF 10 V/m, and 2.5 h for EMF 15 V/m. A similar observation of lag time shortening under the influence of EMF 50 Hz was also reported for the particularly diverse flora of microorganisms from active sludge from wastewater treatment plants [17]. After the lag period, following the multiplication and growth of microalgae, the absorbance of the medium increases accordingly, with the most pronounced increases being recorded in the case of the stimulation with 15 V/m EMF. It was also found that at 40-80 h after inoculation (depending on the intensity of the EMF 50 Hz applied) a limiting trend appears; this can be explained by the decrease in the nutrients' concentration in the culture medium (approximately proportional to the biomass formed). The absorbance is approximately proportional to the concentration of biomass in the suspension. setup for continuous flow production of algal mass. The results show that, for maximum productivity, it is suggested to harvest the algal mass daily in the case of growth stimulation with 15 V/m EMF. At each harvest/sample, it is suggested that the exhausted culture medium be compositionally corrected (by nutrient dosing and pH correction) and revalued by re-introduction into the photobioreactor. The results of the gravimetric determinations, regarding the weighting of the algal mass obtained by filtering 100 mL of suspension and drying the filter, are presented comparatively in Table 1.  
By analyzing the data in Table 1, it is found that after 96 h of culture, by stimulation with 15 V/m EMF, the algal mass concentration in the culture medium is 36.2% higher than that of the reference. Based on the data in Table 1, the average growth rates during the 96 h (4 days) of cultivation can be calculated as 0.47 gdw/L/day for EMF 2 V/m, 0.53 gdw/L/day for EMF 5 V/m, 0.57 gdw/L/day for EMF 10 V/m, and 0.60 gdw/L/day for EMF 15 V/m, compared to only 0.44 gdw/L/day obtained under reference conditions (without exposure of the culture medium to 50 Hz ELF-EMF). The phototropic growth of the algal mass involves the metabolization of CO\({}_{2}\) available in the culture medium--an endothermic process that takes place through enzymatic photocatalysis (h\(\upsilon\)) and through which the conversion of CO\({}_{2}\) into organic (algal) mass takes place with the release of O\({}_{2}\) (2):  
\[2\mathrm{x}\cdot\mathrm{CO}_{2}+2\mathrm{y}\cdot\mathrm{H}_{2}\mathrm{O}+ \mathrm{h}\upsilon\to 2\mathrm{C}_{\mathrm{x}}\mathrm{H}_{\mathrm{y}}\mathrm{O}_{ \mathrm{z}}+(2\mathrm{x}+\mathrm{y}-\mathrm{z})\cdot\mathrm{O}_{2}\mathrm{\uparrow} \tag{2}\]  
The oxygen formed by the process described by Equation (2) is dissolved in the culture medium--the total dissolved oxygen OD (limited by the maximum solubility at the given temperature of 25 \(\pm\) 0.5 \({}^{\circ}\)C) being given by the oxygen released by (2) and part of the oxygen