## 3 Results and Discussion
For this reason, day and night cycles of incident light intensities and temperatures configured to imitate typical Mediterranean climate conditions (repeated summer day in Almeria, Spain, recorded by DLR at Plataforma Solar de Almeria on 15 June 2012, courtesy of [PERSON]) were applied in this study to enable investigation of the growth of _M. salina_ in 16 miniaturized parallel stirred-tank PBRs (Figure 9). One row of 8 parallel PBRs was illuminated with 66% of the incident light intensities, while illumination of the second row followed real-world climate data. Reducing the light intensity to 66% is intended to give an indication of growth in conditions of less sunlight, e.g., due to a cloudy sky. The microalgae displayed behavior that is typical of day and night growth, with biomass formation for as long as light was available and biomass decay when there was no light. No significant differences were observed when following the real Mediterranean climate data compared with the reduced incident light intensities (66%). Mean OD\({}_{750}\) values of 8.96 \(\pm\) 0.84 (100% illumination) and 9.89 +/ - 0.68 (66% illumination), respectively, were measured after 9.5 d. The pH varied between 7.5 and 8.0. The maximum volumetric productivities were reached at Day 6: 0.81 g L\({}^{-1}\) d\({}^{-1}\) (100%) and 0.83 g L\({}^{-1}\) d\({}^{-1}\) (66%), respectively. This corresponds with the results obtained with _M. salina_ in photoautotrophic batch processes at constant incident light intensities of 250-1000 umol m\({}^{-2}\) s\({}^{-1}\) (Figure 5). The maximum volumetric productivities of _M. salina_ observed in the parallel stirred-tank PBRs with day and night cycles are compared to data from the literature (Table 2). Only [PERSON] et al. (2017) reported higher volumetric productivities (4 g L\({}^{-1}\) d\({}^{-1}\)) with the same microalgal strain, climate simulation, and artificial seawater medium. This is due to the smaller layer thickness of 6 mm compared to 35 mm in the parallel stirred-tank PBRs, which enable exponential growth at higher CDW concentrations. \begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Source**} & **CDWmax** & **\(\mu_{\text{opt}}\)** & **Medium** & **Incident Light** & **Layer** \\  & **(g L\({}^{-1}\))** & **(d\({}^{-1}\))** & & & **(umol m\({}^{-2}\) s\({}^{-1}\))** & **Thickness** \\ \hline This work & 3.4 **\(\bullet\)** & 0.525 & _[PERSON]_ & & \\  & (after 6 d) & & (SAG) & ASW & 1000 & 35 \\
[17] & 10 & 0.792 & _[PERSON]. [PERSON]_ & & \\  & (after 7 d) & & (SAG) & ASW & \(\star\) & 6 \\
[30] & 4.5 & & _[PERSON]_ & & \\  & (after 9 d) & & (SAG) & ASW & \(\star\) & 20 \\
[70] & 0.62 & & _[PERSON]_ & ASW, & \\  & (after 8 d) & & (CSIRO) & f/2 & 50 & unknown \\
[72] & 14.2 & 1.3 & _M. salina_ & f/2-Si & 250 & 46 \\
[71] & (after 50 d) & 0.72 & **\(\bullet\)** & f/2 & 290 & 50 \\ \hline \end{tabular}  
* The incident light intensity was not published. ** The CDW concentration was estimated on the basis of the measured OD\({}_{750}\), applying a linear correlation factor of 0.44 g L\({}^{-1}\). ***_Nannochloropsis_ sp.  
\end{table} 
Table 1: Maximum growth rates observed (\(\mu_{\text{opt}}\)) and maximum dry cell weight (CDWmax) concentrations reported for _M. salina_ in photoautotrophic batch cultivations at constant illumination.