Biodiesel Production in Outdoor Cultures of Scenedesmus vacuolatus

The supply of renewable feedstocks for the production of convenience goods combined with the carbon capture and storage is considered a promising solution to both fossil resources depletion and global warming control. Photosynthetic microorganisms, e.g. microalgae, are good candidates for this challenging bet. The culture performances remarkably reduce when microalgal cultures move from laboratory to industrial scale. The basic requisite for the development of large-scale production of oil from microalgae is to make the process environmentally and economically sustainable/feasible. A key issue for the process based on outdoor photobioreactors (PBR) is the efficient utilization of the photosynthetically active radiation (PAR). The present work reports the results of outdoor cultures of Scenedesmus vacuolatus strain ACUF 053/95 in 1.7 L inclined bubble column (IBC) photobioreactors characterized by 250 cm2 irradiated surface. Cultures were carried out in outdoor: i) during the May-July period under shadow conditions, irradiance maximum of 450 μE/(m2 s); ii) during the May-July period under direct sun light, irradiance maximum of 2100 μE/(m2 s); iii) during the September-November period under direct sun light, irradiance maximum of 2000 μE/(m2 s). Harvested microalgae were processed to characterize the biodiesel composition thought direct alkaline transesterification. The biomass concentration at steady state conditions was kept within the range 3-4 g/L. Biomass volumetric productivity ranged in the interval 0.17-0.22 g/(L d) - area specific productivity of 11-15 g/(m2 d) - depending on the operation mode.