Batch growth and β‐carotene production of Dunaliella salina CCAP19/18 was investigated in flat‐plate gas‐lift photobioreactors with a light path of 2 cm, operated in physically simulated outdoor conditions. Dunaliella salina CCAP19/18 showed robust growth with respect to pH 8.0‐9.0 and 15–35°C at increasing salinity, simulating the evaporation of open photobioreactors. The highest β‐carotene concentration of 25 mg L‐1 (3 mg gCDW−1) was observed in batch processes at pH 8.5, 15–30°C and increasing salinity up to 110 g L‐1, simulating a typical Mediterranean summer climate. Intracellular β‐carotene accumulation of D. salina CCAP19/18 was shown to be independent of light availability, although nutrient limitation (K2HPO4, MgSO4, and/or ammonium ferric citrate) seems to enable stable β‐carotene content in the algal cells despite increasing cell densities in the photobioreactor. Fully controlled, lab‐scale photobioreactors simulating typical climate conditions of any region of interest are valuable tools for enabling a realistic characterization of microalgae on a laboratory scale, for production processes projected in open photobioreactor systems (e.g. thin‐layer cascade photobioreactors).

Microalgae are flagged as next-generation biomass feedstock for sustainable chemicals and fuels, because they actively metabolize the climate gas CO, do not impact food production, and are not associated with land-use change. Scaling microalgae cultivation processes from lab to pilot scale is key to assessing their economic and ecologic viability. In this work, process performances of two different Scenedesmus species were studied using a 300 L flat-plate gas-lift photobioreactor system (14 m photosynthetically active area) equipped with a customized, broad-spectrum LED illumination system. Scaling up of batch processes from laboratory scale (1.8 L, 0.09 m) to the geometrically equivalent pilot scale resulted in reduced volumetric biomass productivities of up to 11% and reduced areal biomass productivities of up to 7.5% at the pilot scale. Since biofilm formation was solely detected at pilot scale, biofilm most likely impaired scalability. Nevertheless, repeated addition of nutrients (BG-11) at pilot scale resulted in a 13.5 g L biomass concentration within a 15 day process time with S. obtusiusculus at constant incident-photon flux densities of 1400 µmol photons m s and more than 19.5 g L after 30 days with Scenedesmus ovalternus SAG 52.80 at constant incident-photon flux densities of 750 µmol photons m s. This resulted in areal biomass productivities of 14 g m day (S. ovalternus) and 19 g m day (S. obtusiusculus), respectively.

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