Carbon fixation properties of three alkalihalophilic microalgal strains under high alkalinity

Carbon dioxide (CO2) recovery with high alkalinity microalgal culture is expected to be an energy-efficient and environmentally friendly process. To increase the CO2 recovery efficiency, selection of rapidly growing alkalihalophilic microalgae is necessary. This study optimized the culture conditions of three species of alkalihalophilic microalgae, Arthrospira platensis, Dunaliella salina, and Euhalothece sp., and compared their CO2 fixation potential. Although D. salina tolerated relatively high dissolved inorganic carbon (DIC; 0.50 mol L-1), its carbon fixation rate was found to be slower than the other two species. The two cyanobacteria, A. platensis and Euhalothece sp., favored high pH (9.8-10) and high DIC (0.23-1.1 mol L-1). Euhalothece sp. grew in the highest alkalinity, resulting in the strongest pH buffer against acidification during CO2 absorption. However, the carbon fixation properties of A. platensis and Euhalothece sp. under the same light condition were found to be similar (33 and 35 mmol L-1 day(-1)). These results indicate that the carbon fixation potential per medium inorganic carbon was higher in A. platensis than in the others. Arthrospira platensis was found to be favorable in a CO2 recovery process unless extremely high pH stability is needed.