## 4 Conclusions and Outlook  
New LED illumination modules enabled a commercial MBR system to be operated in an LHS for the photoautotrophic cultivation of microalgae in 48 parallel stirred-tank bioreactors at six different incident light intensities, either with varying constant LED illumination or based on dynamic day and night cycles. This facilitates automated microalgae strain screening and bioprocess development under realistic reaction conditions, even in outdoor applications. In addition to the adapted illumination modules, automated measured liquid levels in the parallel stirred-tank PBRs followed by individual liquid level correction are prerequisites for successful operation to compensate for evaporation because of the long process times of several days up to weeks in batch processes. The parallel \begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Source**} & **CDW\({}_{\text{max}}\)** & **STY\({}_{\text{max}}\)** & **Train** & **Media** & **Illumination** & **Layer Thickness (mm)** \\  & **(g L\({}^{-1}\))** & **(g L\({}^{-1}\) d\({}^{-1}\))** & **Strain** & **Media** & **Illumination** & **Thickness (mm)** \\ \hline \multirow{2}{*}{This work} & 4.0 \({}^{*}\) & \multirow{2}{*}{0.81} & _M. salina_ & \multirow{2}{*}{ASW} & Summer day, & \\  & (after 10 d) & & (SAG) & & Almeria, Spain ** & 35 \\
[17] & 33 & \(\sim\)4 & \(M. salina\) & \multirow{2}{*}{ASW} & Summer day, & \\  & (after 14 d) & & (SAG) & & & \\ \multirow{2}{*}{[73]} & 4.7 & \multirow{2}{*}{0.51} & _N. sp. 211/78_ & & 16 h–8 h & 14 \\  & (after 16 d) & & (CCAP) & & day–night cycles & \\ \multirow{2}{*}{[58]} & 5.5 & \multirow{2}{*}{0.7} & _M. salina_ & \multirow{2}{*}{f/2} & Summer day, & \\  & (after 12 d) & & (SAG) & & Newcastle, & 20 \\ \hline \end{tabular} \({}^{*}\) The CDW concentration was estimated on the basis of the measured OD\({}_{750}\) with a linear correlation factor of 0.44 g L\({}^{-1}\). \({}^{**}\) Recorded by DLR at Plataforma Solar de Almería on 15 June 2012 (courtesy of [PERSON]). \({}^{***}\) Recorded by BSRN station no. 52 on 19 January 2018 [74].  
\end{table} 
Table 2: Maximum volumetric productivities (STY\({}_{\text{max}}\)) and maximum dry cell weight (CDW\({}_{\text{max}}\)) concentrations reported for _M. salina_ in photoautotrophic batch cultivations with day and night cycles. Figure 9: Automated photoautotrophic batch cultivation of _M. salina_ in miniaturized stirred-tank PBRs with day and night cycles imitating typical Mediterranean climate conditions (repeated summer day in Almería, Spain, recorded by DLR at Plataforma Solar de Almería on 15 June 2012, courtesy of [PERSON]). One row of eight stirred PBRs in the bioreaction unit was illuminated at 66% (**left**), and the second row at 100% light intensity (**right**). The gray shading indicates the dynamic incident light intensity variations applied. The temperature of all parallel PBRs was adjusted hourly to follow the climate data. Each bioreactor was initially filled with 10 mL of _M. salina_ suspension in an ASW medium with an initial OD\({}_{750}\) of 0.5 (initial pH 8 + 0.3). Magnetically induced S-stirrers were employed at 500 rpm. The head space of the 48 parallel stirred-tank bioreactors was rinsed with 288 L h\({}^{-1}\) of sterile air with 2% CO\({}_{2}\). Sampling was performed at physically simulated sunrise and sunset times. reproducibility of microalgae growth was in the same order of magnitude compared to heterotrophic bioprocesses with the automated MBRs. This was shown with the example of photoautotrophic growth studies with _M. salina_ with a relative standard deviation of OD\({}_{750}\) of up to 10% at the maximum with the exception of high-photoinhibiting incident light intensities of 1400-1800 \(\mu\)mol m\({}^{-2}\) s\({}^{-1}\). As a consequence, the bioreaction unit in combination with the illumination module has the potential to significantly accelerate bioprocess development with photoautotrophic microorganisms.