## 3 Results and Discussion
### Algal Culture Growth Rates and Biomass Yield under Various Growth Conditions
The benefits of continuous lighting were additionally confirmed by the biomass productivity (Figure 3), final dry weight values, volatile solids, and cell concentration (Table 2). Figure 1: Change of OD\({}_{750}\) during growth of _Scenedesmaceae_ alga, strain EZ-B1, under periodic (**A**) and continuous (**B**) light with various CO\({}_{2}\) concentrations. Thus, the highest biomass productivity was observed at daily PPFD = 112.32 mol m\({}^{-2}\) day\({}^{-1}\) and 2.0% CO\({}_{2}\) and reached 0.69 \(\pm\) 0.02 g L\({}^{-1}\) day\({}^{-1}\). Finally, a daily PPFD of 74.88 mol m\({}^{-2}\) day\({}^{-1}\) and 2% CO\({}_{2}\) (16 h photoperiod) yielded 4.55 \(\pm\) 0.11 g L\({}^{-1}\) of dry weight with a high content of organic matter (4.11 \(\pm\) 0.10 g L\({}^{-1}\)), while the maximum values of dry weight and volatile substances of algal biomass under continuous light were obtained when cultivating alga at 112.32 mol photons m\({}^{-2}\) day\({}^{-1}\) and 2% CO\({}_{2}\) (5.23 \(\pm\) 0.18 g L\({}^{-1}\) and 4.68 \(\pm\) 0.16 g L\({}^{-1}\), respectively). These data show that the light conditions and the concentration of inorganic carbon have a significant effect on the production of algal biomass and are considered species-specific. As many researchers have noted, optimizing the CO\({}_{2}\) concentration when cultivating various algae will both increase the content of metabolic products and optimize cell growth [42; 43; 44]. [PERSON] et al. [45] demonstrated that both the light intensity and an additional CO\({}_{2}\) supply stimulated the growth of _Desmodesumumis_. The optimal values of these parameters were 300 \(\upmu\)mol m\({}^{-2}\) s\({}^{-1}\), which was the maximum tested light intensity, and a supply of 4% CO\({}_{2}\). In a study performed by [PERSON] et al. [46], it was  
Figure 3: Biomass productivity of _Scenedesmacae_ alga, strain EZ-B1, under periodic light (PL) and continuous light (CL). Means that do not share a letter are significantly different (ANOVA, Tukey method, \(\alpha\) = 0.05). Figure 2: Specific growth rate of _Scenedesmacae_ alga, strain EZ-B1, under periodic light (PL) and continuous light (CL). Means that do not share a letter are significantly different (ANOVA, Tukey method, \(\alpha\) = 0.05). noted that a higher light intensity increased the biomass yield of _Chlorella vulgaris_ and _Tetradesmus obliquus_, but since the optimal growth of cultures was observed in the range of 150-300 \(\upmu\)E m\({}^{-2}\) s\({}^{-1}\), it was more appropriate to culture at 150 \(\upmu\)E m\({}^{-2}\) s\({}^{-1}\). The authors also showed that for another culture of the genus _Desmodesmus_, light with an intensity of 300 \(\upmu\)E m\({}^{-2}\) s\({}^{-1}\) was optimal since it significantly increased the biomass yield. In another study, the maximum biomass productivity of _C. vulgaris_ was obtained at a light intensity of 10,000 lux and 2% CO\({}_{2}\) concentration [47]. Maximum biomass yield values during the cultivation of _Scenedesmus dimorphus_ under various parameters were achieved at 15,000 lux and a 12 h photoperiod [48]. [PERSON] et al. [49] evaluated the effect of various CO\({}_{2}\) concentrations ranging from 0.04 to 9% on the growth of several strains of microalgae and cyanobacteria. The growth rate of three strains (_C. vulgaris_, _Chlorella ellipsoidea_, and _Elliputchloris subsphareica_) had a positive correlation with the CO\({}_{2}\) concentration, while high CO\({}_{2}\) had a negative effect on the growth of other strains (_Gloetila pulchra_ and _Arthospira platensis_), which is due to their adaptive mechanisms or features of carbon assimilation. Cultivation of _T. obliquus_ at a 2.5% CO\({}_{2}\) concentration increased the specific growth rate, but at both 2.5% CO\({}_{2}\) and 5.0% CO\({}_{2}\), the maximum biomass concentrations were at the same level [20]. According to a study performed by [PERSON] et al. [50], at higher PPFD values, both the specific growth rate and the biomass yield of _Chlorella sorokiniana_ increased.