# Impact of 50 Hz Electromagnetic Field on the Growth of _Chlorella vulgaris_
## 2 Materials and Methods  
In order to evaluate the influence of 50 Hz EMF on the growth of _Chlorella vulgaris_, comparative determinations were made on samples collected from two identical photo-bioreactors operating with identical parameters (illumination level, temperature, flow rate of air/CO\({}_{2}\) mixture). A reference photobioreactor without exposing the culture medium to EMF was compared to another photobioreactor provided with polarizing electrodes for exposing the culture medium to 50 Hz EMF at various intensities. The experimental setup illustrated in Figure 1 was described in detail in [34]. The equipment diagram is shown in Figure 2.  
Figure 1: The experimental setup. Figure 2: Diagram of the microalgae growth equipment. The culture medium used was BG11 with the following composition: 1.5 g/L NaNO\({}_{3}\); 0.08 g/L K\({}_{2}\)HPO\({}_{4}\); 0.075 g/L MgSO\({}_{4}\)\(\times\)7H\({}_{2}\)O; 0.036 g/L CaCl\({}_{2}\)\(\times\) 2H\({}_{2}\)O; 0.006 g/L citric acid; 0.006 g/L Ferric ammonium citrate green 15% Fe; 0.001 g/L Na\({}_{2}\)EDTA; 0.002 g/L Na\({}_{2}\)CO\({}_{3}\); and compounds for providing microelements: B from 0.00072 g/L H\({}_{3}\)BO\({}_{3}\), Mn from 0.00045 g/L MnCl\({}_{2}\)\(\times\) 4H\({}_{2}\)O, Zn from 0.00045 g/ILZnSO\({}_{4}\)\(\times\) 7H\({}_{2}\)O, Mo from 0.000098 g/L Na\({}_{2}\)MoO\({}_{4}\)\(\times\) 2 H\({}_{2}\)O, Cu from 0.0002 g/L CuSO\({}_{4}\)\(\times\) 5H\({}_{2}\)O, and Co from 0.000013 g/L Co(NO\({}_{3}\))\({}_{2}\)\(\times\) 6H\({}_{2}\)O). The inoculum used to inoculate the culture medium from the two photobioreactors in Figure 1 was _Chlorella vulgaris_ Bienjerrinck CCALA 269 obtained from the Culture Collection of Autotrophic Microorganisms, Trebou, Czech Republic. The working temperature was kept to 25 \(\pm\) 0.5 \({}^{\circ}\)C and was monitored by the temperature sensor incorporated in the type S423/C/OPT oxygen transducer. The intensity of the luminous flux was measured with a portable luxmeter HD2102.1 (equipped with a PHOTON FLOW, PAR LP471 PAR probe, measurement range 0.01-10,000 \(\upmu\)mol/m\({}^{2}\)/s--from Delta Ohm, Padova, Italy) and adjusted using an LED driver (Figure 2) at the level of 310 \(\pm\) 10 \(\upmu\)mol/m\({}^{2}\)/s, light 400 to 700 nm. The bubbles were generated by injecting air mixed with 5% (by volume) CO\({}_{2}\) through a porous hose at 2 L/min, thus resulting in a two-phase flow inside the reactors. The water represents the continuous phase, while the air/CO\({}_{2}\) mixture represents the dispersed phase. The gaseous mixture flow rate was controlled by flow transducers and electrovalves. The intensity and frequency of the EMF applied to the culture medium was controlled by measuring/monitoring the output voltage of the sin-way ELF generator (which was designed and made by the authors) connected to the plane-parallel mounted graphite polarizing electrodes (Figure 2). The experiments were simultaneously performed in the reference reactor and in the experimental reactor, where different electromagnetic field intensities were applied in order to study their influence on the algae growth. Each experiment was carried out on fresh (new) culture medium, both in the reference and in the experimental reactor, and lasted for 96 h. For each of the 4 EMF intensities, 3 determinations were made in the two reactors simultaneously. Thus, under reference conditions, 12 determinations were made. During the growth of _Chlorella vulgaris_, the following parameters were monitored:  
* Evolution over time of pH was monitored by a pH sensor S401 DIG/N type, produced by Chemitec. * Evolution over time of the culture medium turbidity was achieved through the measurement of light absorption in suspension (optical density DO at a wavelength of 750 nm [37; 38]) with a portable spectrophotometer (HACH, Berlin, Germany, DR3900).