## 3 Results and Discussion  
### Comparison of Two Different Raceway Configurations  
_N. oceanica_ growth experiments were performed under three different sets of process conditions (Table 2) in order to determine which of the two raceway configurations were the most promising in terms of productivity, product quality, and energy consumption. Growth kinetics were evaluated separately for each set of process conditions (growth curves are plotted in Supplementary information, Figures 2 and 3). The global areal productivities obtained (Table 3) were higher in the modified raceway for process conditions 1 and 2. Global specific growth rates (Table 3) were similar in both raceways for both the process conditions tested. The range of productivities achieved was half of the value achieved in a demo-scale 530 m\({}^{2}\) raceway ponds using _N. oceanica_ F&M-M24 strain (14 g m\({}^{-2}\) d\({}^{-1}\)) (Mee et al., 2018). de Vree et al. reported average areal productivity of 9.7 g m\({}^{-2}\) d\({}^{-1}\) for _Nannochloropsis_ sp. CCAP 211/78 growth in a raceway pond similar to the one used during the present experiments (25.4 m\({}^{2}\) surface area) with 0.20 m culture depth (S  
The specific growth rates obtained are lower than the range of previously reported data (0.11-0.21 d\({}^{-1}\)) [53]. Nevertheless, the values reported by Baohua et al. [54] for three different _N. oceanica_ strains grown in 8000 L raceway ponds are identical to the ones obtained in this work (0.047 \(\pm\) 0.001 d\({}^{-1}\), 0.066 \(\pm\) 0.005 d\({}^{-1}\), and 0.051 \(\pm\) 0.003 d\({}^{-1}\)). Photosynthetic efficiency (PE) (Table 4) was higher in the modified raceway for process conditions 1 and 2. The higher rotation frequency needed in the modified raceway to attain a given average flow velocity caused a higher turbulence level, enhancing the vertical mixing and the PE of the whole culture. This represents a possible cause for the higher productivities reached in the modified raceway. PE values obtained are comprised in the 0.5-1.5% range of PE reported by de Vree et al. [50] for a _Nannochloropsis_ sp. CCAP 211/78 grown in a 4730 L raceway pond (25.4 m\({}^{2}\) ground area) with a culture depth of 0.20 m and a circulation velocity of 0.25 m s\({}^{-1}\). There were minor differences in the proximate composition (Table 5) and fatty acid profile (Table 6) of the biomass produced in both raceways. The lipid content was lower than the values reported by Das et al. [52] (26.0% \(\pm\) 1.1%) and Baohua et al. [54] (21.40% \(\pm\) 1.53%-28.00% \(\pm\) 1.00%), for _Nannochloropsis_ sp. cultivated in outdoor raceway ponds and three different _N. oceanica_ strains cultivated in indoor raceway ponds, respectively. On the other hand, the values reported by Lopez et al. [36] (12.80% \(\pm\) 3.54%-15.15% \(\pm\) 4.16%) are in the range of the ones achieved in these trials. However, despite the lipid accumulation in _Nannochloropsis_ sp. being strain and species-dependent, it is also conditioned by the culture conditions, varying both with nutritional and environmental factors such as irradiance, nitrogen concentration and salinity [20]. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Photosynthetic Efficiency (\%)**} \\ \hline
**Process Condition/Raceway** & **1** & **2** & **3** \\
**Configuration** & 0.569 & 0.747 & - \\ Standard & 0.532 & 0.674 & 0.618 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Photosynthetic efficiency of _N. oceanica_ cultures obtained when growing in the two raceways tested. Values represent an average of two biological replicates.