Response surface optimization for outdoor cultivation of Isochrysis galbana in a PV-integrated photobioreactor

Managing light effectively is one of the biggest challenges in outdoor microalgal cultivation, especially under the rapidly shifting sunlight typical of tropical climates. In this study, we used Response Surface Methodology (RSM) to understand how light conditions, controlled by distance from a PV-integrated LED system and the presence or absence of LED supplementation, shape the growth of Isochrysis galbana. A Central Composite Design was applied to evaluate how these factors influence PPFD, biomass production, maximum specific growth rate (μmax), and culture temperature. The fitted RSM models performed well, showing close agreement between predicted and measured values. LED supplementation consistently increased PPFD, while distance was the most significant factor affecting light delivery. Based on numerical optimization, the model identified an optimal irradiance of around 1680 μmol photons m−2 s−1 at temperatures of 31–33 °C. These predicted conditions were then verified through outdoor experiments, which produced high biomass (0.913 g L−1) and rapid growth (μmax = 0.92 day−1) using only ambient air. This confirms that Isochrysis galbana can achieve strong performance without CO2 enrichment when light and temperature are managed effectively. Overall, the study shows that combining outdoor trials with RSM offers a powerful way to fine-tune light availability and improve the efficiency of low-energy, PV–LED-assisted photobioreactor systems. The findings provide practical guidance for scaling up sustainable microalgae cultivation in sun-rich regions.

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