CO2 capture and production of biomolecules in a microalgal airlift photobioreactor operated under different hydrodynamic conditions and in presence or in absence of a static magnetic field

This study evaluated the combined effect of superficial gas velocity ( U g ), bubble diameter ( d B ), and exposure to a static magnetic field (SMF) on CO 2 fixation capacity (FC), its gas – liquid mass transfer ( k L a ), and biomolecule accumulation in a steady-state AirLift photobioreactor (ARL). Ten treatments were analyzed, derived from five U g – d B combinations under 45 mT and their respective control reactor. Hydrodynamic parameters were estimated through high – resolution image analysis and theoretical modeling based on Higbie's penetration theory. Experimental k L a values ranged between 0.003 and 0.008 s −1 , showing a positive correlation with U g (ρ = +0.88, p < 0.05 ). The highest theoretical value estimated using Higbie's model was 0.0085 s −1 with a d B = 2.6 mm, validating its applicability in diffusion – dominated systems. However, conditions with higher experimental k L a did not always lead to greater FC, suggesting the existence of a biological reaction – controlled zone. The multifactorial ANOVA indicated significant effects of U g and SMF on both FC and experimental k L a ( p < 0.05 ), with SMF being the primary factor influencing FC variation. Lipid, chlorophyll, and carotenoid accumulation was favored under SMF exposure in conditions with small bubbles and low U g . Finally, the novelty of this work relies on the demonstration that hydrodynamic parameters not only affect gas transport and consumption, but also the synthesis of biomolecules of interest. • Higbie's model predicted CO 2 k L a for bubble diameters <3 mm. • Experimental k L a increased with U g , confirming its influence on multiphase systems. • CO 2 fixation capacity was primarily influenced by SMF exposure. • SMF and low U g – d B enhanced biomolecule production.