Bioprocess modelling assisted analysis of light and temperature effects on Dunaliella tertiolecta’s growth in bicarbonate/carbonate medium for algae-based carbon capture

Industrial upscaling of algae-based carbon capture based on gaseous CO 2 substrate faces challenges related to CO 2 transport, storage, dissolution and leakages. The use of an indirect bicarbonate/carbonate system to shuttle carbon to the culture offers a flexible alternative, though their high pH and hypersalinity limits compatibility with many strains. Dunaliella tertiolecta, however, produces high concentrations of glycerol to balance osmotic pressure and regenerate carbonate, lowering sequestration costs. Yet, complex interactions between light intensity and temperature complicates long-term closed-looped bicarbonate/carbonate operations. Therefore, this study utilises experimental datasets across three light intensities (5200 Lux, 10400 Lux, and 26400 Lux) and four temperatures (15 °C, 20 °C, 24 °C, and 28 °C) to derive bioprocess insights and develop dynamic biokinetic models for biomass growth, sodium bicarbonate assimilation and sodium carbonate regeneration- the first for any Dunaliella species. Biomass growth dynamics, inversely proportional to high sodium bicarbonate levels due to nutrient limitations, was modelled using the Contois structure, achieving a 12.7 % overall average error against experimental datasets. Optimal conditions at 20 °C and 5200 Lux yielded a maximum specific growth rate of 0.027 h⁻¹ , bicarbonate conversion of 43.57 g g −1 , and carbonate regeneration of 75.47 g g −1 , sustaining bioprocess dynamics for up to 270 hrs without nutrient supplementation. Beyond this point, unused assimilated CO 2 leaks from the cytoplasm, reacidifying the growth media and impairing carbonate regeneration- a phenomenon not previously detailed in Dunaliella tertiolecta . These findings deepen our understanding of closed-loop biological CO 2 sequestration and inform future optimisation and industrial application. • Bicarbonate offers a versatile alternative for algae-based CO 2 sequestration. • D. tertiolecta tolerates high pH, hypersalinity and renews absorbent carbonate. • Light and temperature strongly affects D. tertiolecta’s bioprocess performance. • Optimal bioprocess conditions were identified at 20 °C and 5200 Lux. • Closed-loop recirculation limited by nutrient supply during extended operation.