Physiological changes in carbon sequestration and lipid production characteristics of microalgae under high CO₂...

Carbon dioxide utilization is a key component of carbon capture, utilization, and storage (CCUS) technology, with oil-producing microalgae-based carbon sequestration being particularly efficient. This study investigated the carbon sequestration potential and lipid metabolism of three marine microalgae (Chlorella sp., Isochrysis galbana, and Nannochloropsis oceanica) under CO₂ concentrations ranging from 10% to 25%, covering typical industrial flue gas levels. The results showed that microalgae exhibited higher utilization efficiency at lower CO₂ concentrations. Notably, Nannochloropsis oceanica demonstrated strong CO₂ tolerance, maintaining a specific growth rate of 0.108 day⁻¹ even at 25% CO₂, with a biomass productivity of 0.03454 g·L⁻¹·day⁻¹-11.42% higher than Chlorella sp. and 7.23% higher than Isochrysis galbana. Under 10% CO₂ conditions, its carbon sequestration efficiency and CO₂ utilization rate reached 0.110 g CO₂·L⁻¹·day⁻¹ and 2.15%, respectively, while Rubisco enzyme activity increased by 52.6%, indicating highly efficient carbon assimilation. Under 25% CO₂ stimulation, the total lipid content of Nannochloropsis oceanica increased to 53.93%, surpassing Chlorella sp. (52.53%) and Isochrysis galbana (46.69%). The lipid profile showed 40.95% monounsaturated fatty acids and 28.82% eicosapentaenoic acid (EPA), demonstrating its potential for both bioenergy and high-value product development. This study systematically explores the growth lifecycle of microalgae under high CO₂ environments, providing scientific insights into their carbon sequestration mechanisms and physiological responses, thereby offering valuable references for developing microalgae-based flue gas carbon sequestration technologies.