A robust multi-nutrient kinetic model for enhanced lutein and biomass yields in mixotrophic microalgae cultivation -- A step towards successful large-scale productions

Mixotrophic cultivation holds great promise for enhanced biomass production and valuable metabolite synthesis from microalgae. This study introduces a versatile kinetic model encompassing the most influential factors, while emphasizing on lutein production, a highly sought-after bioproduct. This most extensive study to date incorporates multi-nutrient kinetics for Tetradesmus obliquus in mixotrophic regime, covering various nutritional conditions. Crucial nutrients governing the model include nitrate, phosphate, and glucose. Using 7 state variables and 13 unknown parameters, the model’s accuracy was ensured through a well-designed 2-factor, 4-level experimental setup, providing ample data for reliable calibration and validation. Results show high accuracy in predicting dynamic concentration profiles for all validation experiments, revealing wide applicability. Optimizing nitrogen availability led to significant increases in biomass (up to 4-fold) and lutein production (up to 12-fold), with observed maximum biomass concentration of 6.80 g.L and lutein reaching 25.58 mg.L . Noticeably, the model exhibits a maximum specific growth rate of 4.03 day , surpassing reported values for photoautotrophic and heterotrophic conditions, suggesting synergistic effects. Valuable guidance is provided for applying the method to various microalgal species and results are large-scale production-ready. Future work will focus on exploiting these results for developing real-time photobioreactor operation strategies.