## 4 Results and Discussion
### Biochemical Analysis  
After growth, all the batch cultures were harvested, lyophilized and the biomass was employed to perform biochemical analysis. Results are shown in Figures 7-9. Figure 8: Biochemical composition of the biomass obtained at the end of the batch cultivations grown under different conditions: (**a**) quasi-isoactinic reactor with different photon flux densities; (**b**) reactors with different configurations at incident light intensity \(I_{0}=210\)\(\mu\)E s\({}^{-1}\)m\({}^{-2}\). Figure 7: Batch productivity of the cultures grown in different conditions: (**a**) quasi-isoactinic reactor with different photon flux densities; (**b**) reactors with different configurations at incident light intensity \(I_{0}=210\)\(\mu\)E s\({}^{-1}\)m\({}^{-2}\). Figure 7 reports the batch productivity in terms of grams of dry weight per liter per day of cultivation. The biomass productivity ranges from 0.3 g L\({}^{-1}\) d\({}^{-1}\) to 1.2 g L\({}^{-1}\) d\({}^{-1}\) of the culture grown under 210 uE s\({}^{-1}\)m\({}^{-2}\). As expected, the productivity increases with the incident photon flux density, as shown in Figure 7a. At the same time, the productivity decreases with the reactor thickness, as shown in Figure 7b. This is a consequence of the fact that the average light intensity is lower when the reactor thickness increases, and therefore the volumetric productivity diminishes because of the lack of light as substrate. Other studies in the literature report batch productivity of _Nannochloropsis_ in different cultivation conditions [25,26]. The productivities reported in the present study are in general significantly higher and this is due to the high average light intensity distributed inside the flat and the annular reactors employed in the present work. Figure 8 shows the biochemical composition of the biomass obtained at the end of the batch cultivations and grown under different photon flux densities (Figure 8a) and in reactors with different configurations (Figure 8b). Lipid content shows a defined trend between the analysed conditions, while carbohydrate and protein content do not. Carbohydrate content is on average around 8% of the dry weight, while protein content is on average around 20% of the dry weight, as previously determined in the same strain [27]. _Nannochloropsis_ is considered to be one of the most promising genera of microalgae in the production of lipids because of the possibility of accumulating high contents of up to 60% [28]. In this work, _Nannochloropsis gaditana_ accumulated lipids from 9% of dry weight of the biomass grown under 20 uE s\({}^{-1}\)m\({}^{-2}\) up to 45% of the dry weight of the biomass grown under 450 uE s\({}^{-1}\)m\({}^{-2}\), similarly to that previously reported for the same strain [22,27]. The content of lipids increases with the average light intensity inside the reactor, both when cells were cultivated in the quasi-isoactinic reactor with increasing light intensity (Figure 8a) and when cells were cultivated in reactors with different geometries (Figure 8b). This trend was already observed before but, in this case, we report an accurate analysis with several different changing inputs in the cultivation [26,29]. This is the first time that a complete biochemical analysis was performed on biomass cultivated in quasi-isoactinic conditions. Figure 9: Fatty acid analysis as percentage of total fatty acid content in the biomass obtained at the end of the batch cultivations grown under different conditions: (**a**) quasi-isoactinic reactor with different photon flux densities; (**b**) reactors with different configurations at incident light intensity \(I_{0}=210\) uE s\({}^{-1}\)m\({}^{-2}\). SFA, saturated fatty acid; MUFA, monounsaturated fatty acids; PUFA: polyunsaturatedated fatty acid. Analysis of the fatty acids content was performed in the same way and results are shown in Figure 9 and in Table 3.  
The fatty acid class composition varies when growing microalgae under different photon flux densities and in different geometries.