Studies on the scale-up of biomass production with Scenedesmus spp. in flat-plate gas-lift photobioreactors

Abstract: Microalgae are flagged as next-generation biomass feedstock for sustainable chemicals and fuels, because they actively metabolize the climate gas CO₂, 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 m² 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 m²) 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_CDW L⁻¹ biomass concentration within a 15 day process time with S. obtusiusculus at constant incident-photon flux densities of 1400 µmol photons m⁻² s⁻¹ and more than 19.5 g_CDW L¹ after 30 days with Scenedesmus ovalternus SAG 52.80 at constant incident-photon flux densities of 750 µmol photons m⁻² s⁻¹. This resulted in areal biomass productivities of 14 g_CDW m⁻² day⁻¹ (S. ovalternus) and 19 g_CDW m⁻² day⁻¹ (S. obtusiusculus), respectively.