Stability of carbohydrate production in continuous microalgal cultivtion under nitrogen limitation: Effect of irradiation regime and intensity on Scenedesmus obliquus

In this work, the effect of nitrogen limitation on Tetradesmus (Scenedesmus) obliquus cultivation was evaluated in a continuous system operated at steady-state to assess the carbohydrate productivity in a single step. Under continuous irradiance (150 and 650 μmol photons m−2 s−1), with an optimized nitrogen limitation in the reactor inlet stream, a carbohydrate fraction of 45% was achieved, with a remarkable productivity of 0.80 g L−1 day−1. Under simulated day-night irradiation, a cyclic steady state was obtained, as a result of alternating light and dark conditions, with an average carbohydrate production of 0.71 and 0.30 g L−1 day−1 (summer and winter, respectively), with a biomass productivity reduced due to the photoperiod. The uptake of nutrient by the cell appeared to be regulated by the light regime, which determines the carbohydrate accumulation as well. Accordingly, it was possible to obtain a stable carbohydrate production in one-step continuous system with day-night and seasonal irradiation by properly managing the nitrogen inlet.