# Impact of 50 Hz Electromagnetic Field on the Growth of _Chlorella vulgaris_
## 4 Conclusions  
Through experimental determinations, the influence of ELF-EMF of 50 Hz on the microalgae _Chorella vulgaris_ growth in BG11 culture medium was studied. The experimental determinations were made simultaneously in two photobioreactors with identical geometry at identical operating parameters (25 \(\pm\) 0.5 \({}^{\circ}\)C temperature, 310 \(\pm\) 10 \(\upmu\)mol/m\({}^{2}\)/s--light 400 to 700 nm, 2 L/minute dispersed mixture of air with 5% CO\({}_{2}\) by volume), one reference and one equipped with graphite electrodes placed in parallel planes connected to a sin-way ELF generator with adjustable output voltage to create a controlled and homogeneous EMF on the culture medium. The results of spectrophotometric and gravimetric determinations showed the following:  
* The reference lag period lasts approximately 8 h and is reduced as the 50 Hz EMF intensity increases to approx. 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;
* The average growth rates in the 96 h of cultivation were 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;
* After the lag period, the growth rates of the algal mass increase to a maximum at 80 h from inoculation to the reference and faster at 72 h for 2 V/m EMF, 40 h for 5 V/m EMF, 32 h for 10 V/m, and 24 h for EMF 15 V/cm;
* The maximum growth rate of the algal mass at 15 V/m is 2.75 times higher than that recorded in the reference. The registered values of dissolved oxygen concentration (OD) in the culture medium showed that after LAG time, OD has a period of growth in which the growth rates are consistent with the growth speed of the algal mass, after which it shows a trend of limitation to the maximum solubility of oxygen. The results of the chemical analysis for the concentrations of N-NO\({}_{3}\), TN\({}_{\text{b}}\) (total nitrogen), and Pt (total phosphorus) showed the following:  
* Following the increase in algal mass, the N-NO\({}_{3}\) content of the BG11 culture medium decreases by 58 mg/L/day at 15 V/m EMF compared to 43 mg/L in the reference;
* Following the increase in algal mass, the Pt content of BG11 decreases to 90% depletion after approx. 80 h at baseline versus only 48 h of growth by exposure to 15 V/m ELF;  
Figure 9: The influence of 50 Hz EMF intensity on the nitrogen and phosphorus content of the algal mass. Following the increase in algal mass, the increase in TN\({}_{\rm b}\) in 96 h was 8 mg/L and 115 mg/L at 15 V/m EMF (14 times higher), showing that the influence of the EMF increases with its intensity; - The nitrogen content of the algal mass obtained after 96 h of culture increases linearly depending on the applied EMF intensity from 8.47% (reference) to 12.12% for 15 V/m EMF; - The phosphorus content of the algal mass obtained after 96 h of culture decreases from 0.77% (reference) to 0.57% for 15 V/m EMF. These results lead to the conclusion that the EMF of 50 Hz stimulates the growth of _Chorella vulgaris_ (maximum growth rate 2.75 times higher than the reference) in a BG11 culture medium, whose P\({}_{\rm t}\) reserves are depleted approx. 2 times faster than in reference conditions. The depletion of 90% of the P\({}_{\rm t}\) resource in the culture medium results in the cessation of the proliferation of algal biomass. The 15 V/m EMF stimulates the ability to accelerate the nitrate assimilation, the increase in TN\({}_{\rm b}\) being 14 times higher than in the reference. Exposure to EMF 50 Hz leads to changes in the phosphorus and nitrogen content (concentration) of the algal mass.