## 1 Introduction
Our research work aimed to identify the combined effects of light regimens and CO\({}_{2}\) concentrations on the growth of newly isolated indigenous microcalga within the family _Scenedesmacae_. Additionally, the biochemical composition of the cells and nutrient removal by cells from the synthetic nutrient medium were studied. It has previously been shown that a variety of microalgae of the family _Scenedesmacae_ can be used as agents for removing inorganic nutrients from contaminated waters [26], promising sources of valuable products, CO\({}_{2}\) fixation agents, and as feed substitutes [27; 28]. The selection of optimal growth conditions for algae of the family _Scenedesmacae_ has been the focus of many research groups [20; 21; 22; 27; 28; 29]. However, many studies have been conducted using a narrow range of conditions or have optimized their growth using only one parameter. Thus, in the work of [PERSON] and [PERSON] [29], the cultivation of an indigenous species, _Tetradesmus bajcalifornicus_, was carried out at different CO\({}_{2}\) concentrations but at a constant light intensity (180 \(\mu\)mol m\({}^{-2}\) s\({}^{-1}\)). The authors noted a significant effect of CO\({}_{2}\) concentration on the growth and biochemical composition of the cells. In another work [20], _Tetradesmus obliquus_, along with representatives of the genus _Chlorella_, were cultured in a glass bubble column photobioreactor at 74 \(\mu\)mol m\({}^{-2}\) s\({}^{-1}\) and at various CO\({}_{2}\) concentrations. Among the tested microalgae, _T. obliquus_ had high growth parameters and lipid production levels, and the authors noted that _T. obliquus_ showed high adaptation to elevated levels of CO\({}_{2}\). Among the studies devoted to the study of the influence of light on microalgae of the family _Scenedesmacae_, there are few studies where high levels of PPFD were tested. In many studies, the PPFD values rarely exceed 150 \(\mu\)mol m\({}^{-2}\) s\({}^{-1}\)[20; 29; 30; 31; 32], which does not allow to fully evaluate the capabilities of the algae. A previous study demonstrated that the novel _Scenedesmacae_ microcalga, strain EZ-B1, accumulated a high protein level when grown in diluted anaerobic digester effluent, a residue of anaerobic digesters [33]. In the present study, we aimed to study the effect of high PPFD on the metabolism of this microcalga, considering that high PPFD is a metabolic shift strategy to increase the synthesis of certain products, including pigments [24; 34]. Considering that the high tested light intensities can cause photoinhibition of microalgae [35], in this work, cultivation was carried out both under continuous and periodic light. It is also known that the use of different photoperiods makes it possible to change the biochemical composition of microalgal cells [9; 36]. A series of experiments were carried out to analyze the effects of daily PPFD (37.44-112.32 mol m\({}^{-2}\) day\({}^{-1}\)), photoperiods (16 h and 24 h), and various CO\({}_{2}\) concentrations (1-4%) on algal growth, biomass productivity, nutrient removal, and accumulation of selected metabolic products in a well-controlled Labfors 4 Lux photobioreactor.