Development of an Effective Microalgae Cultivation System Utilizing CO 2 in the Air by Injecting CaCO 3

Recognized as the third-generation biomass of the future, microalgae are increasingly viewed as a promising solution for the sustainable production of biofuels, often referred to as “green gold.” Extensive research is being conducted across the upstream, midstream, and downstream sectors to develop fundamental technologies that enable efficient and economical large-scale microalgae cultivation. Recent studies suggest that microalgae-based biofuels have the potential to meet global energy demands. However, challenges such as spatial constraints in site selection and the high cost of transporting CO 2 —an essential component for pH regulation and photosynthesis—pose obstacles. Here, this study demonstrates that by supplementing air-only medium with CaCO 3 , Chlorella sorokiniana can effectively utilize airborne CO 2 to produce biomass. In laboratory-scale culture conditions supplied only with air, adding 5 mM CaCO 3 (pH 7.8) could maintain the pH stably compared to the untreated conditions (pH 9.5) and improved the biomass concentration and lipid content by 17.68-fold and 9.58-fold, respectively. In bench-scale conditions, cultures supplemented with 5 mM CaCO 3 exhibited a 9-fold increase in the biomass and a 7.15-fold increase in the lipid concentrations compared to those cultivated with air alone. With microalgae emerging as an essential resource for future generations, cultivation technology utilizing CaCO 3 will be a critical technology that enables commercial-scale microalgae cultivation using only air, without artificial CO 2 supply facilities.