Bicarbonate-based cultivation of Chlorella sorokiniana SU-1: Optimizing culture conditions and utilizing bicarbonate from flue gas chemical absorption

Integrating bicarbonate-based carbon capture with algae production presents a viable solution for Carbon Capture, Utilization, and Storage (CCUS). This study investigates the growth of Chlorella sorokiniana SU-1, a model microalgal strain, in a bicarbonate-enriched medium. The research focuses on optimizing cultivation conditions by examining different bicarbonate concentrations (1–20 g/L KHCO₃), pH levels (7.5, 8.5, 9.5), and nitrogen sources (NaNO₃, NH₄Cl, NH₄HCO₃). Results show that C. sorokiniana SU-1 achieved its highest bicarbonate consumption efficiency (84.5 %) and biomass concentration (1.022 g/L) in a medium containing 5 g/L KHCO₃ and 1.5 g/L NaNO₃ at pH 8.5. Additionally, the kinetic model predicts the maximum specific growth rate at a bicarbonate concentration of 5.980 g/L. When replacing CO₂ with bicarbonate ions as the inorganic carbon source, the total carbohydrate content decreased from 44.4 % to 23.9 %, while protein content increased from 39.6 % to 52.8 %. The study also found that because CO₂ is less soluble in water compared to bicarbonate ions, the carbon utilization efficiency of the SU-1 strain was only 11.1 % for carbon dioxide, significantly lower than the 86.9 % observed for bicarbonate ions. Furthermore, the research examined microalgal growth using KHCO₃ obtained through alkali absorption of factory flue gas. At bicarbonate concentrations of 1 and 6 g/L KHCO₃, C. sorokiniana SU-1 consumed over 80 % of the chemically absorbed bicarbonate. These findings demonstrate the feasibility of cultivating microalgae in bicarbonate-based media, underlining its potential for future commercial applications in CCUS.