Carbohydrate productivity in continuous reactor under nitrogen limitation: effect of light and residence time on nutrient uptake in Chlorella vulgaris

Chlorella vulgaris is commonly recognized as an interesting species for bioethanol production due to itscarbohydrate content. Carbohydrates accumulation is often obtained under nitrogen starvation, which onthe other hand may lead to a reduced biomass production. In this work, the effect of nitrogen limitation ina continuous system was assessed, with the aim of finding an optimal value where biomass productivityand carbohydrate content are well balanced. The effect of light intensity was also investigated, and it was highlighted that in a continuous system light stress is the main variable affecting the carbohydrate content and productivity. It was also evidenced that increasing the residence time is a way to boostnitrogen starvation: the biomass yield on nitrogen noticeably changes with the residence time, thus modifying the elemental composition of the microalgal biomass, and resulting in an accumulation ofcarbohydrates.