Integrating Spirulina cultivation as a bioregeneration step in a closed loop CO2 absorption process: Experimental validation

The integration of microalgal cultivation with CO₂ capture via chemical scrubbing can improve carbon utilization efficiency while reducing operational costs. However, the reciprocal effects between absorption and cultivation units need further investigation. This study evaluated the integration of carbonate-based CO₂ capture with cultivation of the alkaliphilic cyanobacterium Spirulina sp. in a Bicarbonate-based Carbon Capture and Algae Production System (BICCAPS). The effects of bicarbonate concentration, air sparging, medium recycling and absorption promoters were investigated experimentally, and the absorption step was assessed through Aspen Plus simulations. Air sparging removal did not significantly affect biomass concentration. Increasing sodium bicarbonate to 0.54 mol L −1 maximized steady-state biomass concentration, whereas 0.72 mol L⁻¹ inhibited growth. Complete medium recycling progressively reduced biomass productivity, likely due to exopolysaccharide (EPS) accumulation, although CO₂ absorption kinetics were not significantly affected. In continuous operation, 85% medium recovery sustained biomass concentrations comparable to the no-recycle control, but reduced phycobiliprotein content; conversely, 90% recovery promoted excessive EPS accumulation and culture instability. Boric acid and triethanolamine negatively affected growth, although partial adaptation to prolonged exposure was observed. Absorption simulations indicated that increasing K₂CO₃ concentration from 1.5 to 4 wt%, while producing inorganic carbon levels compatible with cyanobacterial growth, reduced both absorber diameter and solvent flow rate relative to the reference condition. Overall, these results support the potential of bicarbonate-based microalgal cultivation in integrated carbon capture processes and identify bicarbonate tolerance, EPS accumulation, medium recycling and promoter toxicity as key parameters for BICCAPS optimization.