Modeling of dynamics of nitrogenous compounds in microalgae cells. 1. Batch culture

The work is focused on modeling of dynamics of nitrogenous compounds in microalgae cells. The model is based on the idea that all intracellular nitrogen can be considered as the sum of structural and reserve forms. The rate of nitrogen supply into the cell and the rate of its consumption for the synthesis of structural components are described in the form of linear splines and expressed through the ratio of reserve and structural forms. It is shown that species-specific parameters of the model are light-dependent values. Particular integrated solutions have been found for specific cases of nitrogen supply. The dynamics of all forms of intracellular nitrogen and nitrogen concentration in the medium follow the exponential law. The mathematical model for quantitative description of microalgae culture growth in the absence of nitrogen in the environment is proposed. The equations obtained using experimental data on the culture growth and nitrogen assimilation by cells of green microalgae Dunaliella salina and Scenedesmus obliquus have been verified. The proposed model allows to describe the dynamics of the concentration changes of structural, reserve and extracellular nitrogen in the cultivation of these species. For the exponential growth phase, the species-specific coefficients of the maximum specific rate of nitrogen supply into the cell and the maximum specific rate of the synthesis of structural components, which for D. salina amounted to: 0.42 day$^{-1}$ and 0.55 day$^{-1}$; for S. obliquus — 1.37 day$^{-1}$ and 1.25 day$^{-1}$ respectively have been determined. Differences of these parameters for two types of microalgae are due to different light conditions of their cultivation.