A mathematical model of microalgae growth in a pilot scale thin-layer photobioreactor

Thin-layer photobioreactors represent a promising technology for high-productivity microalgae cultivation, yet their scale-up and optimization remain limited by the lack of validated dynamic models. In this work, a comprehensive first-principles dynamic model describing the growth of Nannochloropsis gaditana in a pilot-scale thin-layer photobioreactor (2.4 m3, 63 m2 illuminated surface, 0.023 m liquid depth) is developed, calibrated, and validated for the first time. The model integrates biological kinetics with mass and energy balances, explicitly accounting for photosynthetically active radiation, ambient temperature, gas–liquid mass transfer, CO₂ injection, and oxygen stripping. Model predictions accurately reproduce the temporal evolution of biomass concentration, pH (7.5–8.5), temperature (15–27 °C), and dissolved oxygen (up to 200% air saturation) under outdoor operating conditions. Validation against independent experimental data confirms the predictive capability of the model under both batch and semi-continuous regimes. Model-based analysis indicated that dissolved oxygen accumulation acts as a measurable inhibitory factor affecting photosynthetic activity along the thin-layer channel. Although local oxygen inhibition may reduce photosynthetic activity by up to 50% during peak daylight hours, its overall impact on daily biomass productivity under the operating conditions investigated remained moderate. Simulations predicted that maintaining dissolved oxygen concentrations close to air saturation through enhanced oxygen stripping would increase biomass productivity by approximately 5%. In contrast, dilution rate optimization emerged as the most effective operational strategy, with theoretical productivity improvements of up to 70–95%, while more practical operating conditions were predicted to increase productivity by approximately 45–60% relative to the baseline operation. This study provides the first dynamic model validated at pilot scale for thin-layer photobioreactors, offering a robust tool for their design, optimization, and control toward large-scale microalgae production.