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 300L flat-plate gas-lift photobioreactor system (14m2 photosynthetically active area) equipped with a customized, broad-spectrum LED illumination system. Scaling up of batch processes from laboratory scale (1.8L, 0.09m2) 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 gCDW L-1 biomass concentration within a 15day process time with S. obtusiusculus at constant incident-photon flux densities of 1400µmol photons m-2 s-1 and more than 19.5 gCDW L1 after 30 days with Scenedesmus ovalternus SAG 52.80at constant incident-photon flux densities of 750µmol photons m-2 s-1. This resulted in areal biomass productivities of 14 gCDW m-2 day-1 (S. ovalternus) and 19 gCDW m-2 day-1 (S. obtusiusculus), respectively.