Beyond CO2: Incorporating Bicarbonate, Dynamic Carbon Speciation, and Stoichiometric Plasticity Into Algal Growth Models.

The design of biological carbon capture systems to uptake carbon dioxide by photoautotrophic cultivation of algae has been proposed to mitigate atmospheric carbon emissions. Multiple models to predict algal growth as a function of nutrients have been proposed, but few have delved into the complex dynamic reactions of algal growth as influenced by individual inorganic carbon species. In this work, dynamic algal growth models based on inorganic carbon-limited specific growth rates that considered carbon dioxide (CO2), bicarbonate (HCO3 -) and carbonate (CO3 2-) as potential substrates in Monod model equations were investigated and compared to batch, closed reactor data. The model incorporates dynamic rates of inorganic carbon species conversion rather than equilibrium conditions and algal biomass stoichiometry that accounts for algal plasticity as a function of nutrient concentration. After analysis of 8 models, the model that included CO2 and HCO3 - as substitutable substrates is best supported by literature and provided the best estimates of total inorganic carbon concentrations, biomass, and pH for a set of experimental cultures. These results provide a grounded framework for predicting algal growth and carbon speciation, thereby informing the design and operation of algal cultivation systems for carbon abatement and bioproduct formation under carbon-limited, low-light, and high-pH conditions.