Modeling Biomass Growth and Nitrogen Fixation by Heterocystous Cyanobacteria Cultivated in Continuous Photobioreactors

Nitrogen-fixing cyanobacteria application in bioprocesses holds the potential for enhanced bioindustry sustainability. To address challenges hindering microalgae-based processes scale-up, integrating empirical evidence with suitable kinetic models is crucial. Microalgae kinetic growth models usually disregard unique features of diazotrophic species, whose growth depends on both light intensity and dinitrogen availability. This work introduces a kinetic model separately describing vegetative cells and heterocyst growth, along with nitrogen accumulation in biomass, which was then validated on continuous cultivation data of two heterocystous species, namely, Anabaena and Nostoc. An experimental modeling-integrated approach was applied for species- and system-specific kinetic parameter retrieval. The lack of data on the effect of dissolved dinitrogen limitation in continuous systems was addressed by varying N2 partial pressures, demonstrating Nostoc promising N-fixation capabilities when N2 is not limiting compared to a combined nitrogen supply. The model accurately predicts how residence time, light, and nitrogen availability affect the growth of different species, encompassing both diazotrophic culture and combined nitrogen supply.