Nitrogen to biomass, chlorophyll and carotenoids transfer functions for microalgae Scenedesmus sp.

Mayor nutrients in autotrophic growth are solar energy, carbon dioxide, nitrogen as nitrates or as ammonia, and other macro and micronutrients. Some microalgae products with a high commercial value require a certain concentration of nitrogen to be reached or maintained in the medium during cultivation. For example, Haematoccocus pluvialis is used to produce astaxanthin (a secondary metabolite) and requires first a growth stage with high nitrogen concentrations, and then an induction stage with nitrogen deprivation in the medium. In the case of Scenedesmus used to produce lutein (primary metabolite), it is necessary to maintain nitrogen concentrations in the medium above a certain concentration in order to promote production and accumulation of lutein in the biomass. Nitrogen concentration for lutein production is usually determined by experimentation to be suitable for the species being used and culture conditions. In several species of microalgae biomass maximum concentration is also influenced by nitrogen concentrations in the medium. In the present article we present transfer functions of nitrogen cultivation associated with biomass and pigment production under autotrophic conditions in batch and fed batch culture modes. Transfer-function representations are presented in the document and compared to experimental data and discussed. Transfer function complexity increased with increased nitrogen level in both culture modes. Control theory can be used in microalgae cultures to model behavior in response to nutrients such as nitrogen. With the proper data and transfer function, nitrogen modeling and control may be achieved in microalgae cultivations for biomass and high value molecules production.