Year-long production of Scenedesmus almeriensis in pilot-scale raceway and thin-layer cascade photobioreactors

Abstract

Biomass of Scenedesmus almeriensis was produced outdoors for 12 months using three different photobioreactor designs. Optimum dilution rates to achieve the highest biomass productivities were 0.2 day-1 for raceways and 0.3 day-1 for thin-layer reactors. Biomass productivities achieved using thin-layer cascade photobioreactors during the months of higher photosynthetic activity reached 30-35 g/m2·day, higher than those obtained using raceways during the same period: 20-25 g/m2·day. Photosynthetic efficiency was lower in spring/summer when compared to autumn/winter, suggesting that a larger share of the solar energy that reaches the culture in spring/summer is not used for microalgal growth. During summer, culture temperature reached 40 °C in thin-layer photobioreactors, which demonstrates the importance of selecting microalgal strains able to resist these conditions. Photoinhibition was not observed at incident irradiances up to 1600 μE/m2·s. However, dissolved oxygen values were especially high in thin-layer photobioreactors during this time of the year. They reached maximum values of 400% and showed an inhibitory effect on microalgal growth.