New insights into the CO2-steady and pH-steady cultivations of two microalgae based on continuous online parameter monitoring

CO2-steady and pH-steady cultivations are two common strategies used in the cultivation of microalgae for the control of carbon supply. However, the differences between the two strategies have seldom been discussed due to the lack of an appropriate evaluation platform. Here, a precise comparison of CO2-steady and pH-steady modes was carried out using Nannochloropsis oceanica IMTE1 and Isochrysis zhangjiangensis on the Algal Station system, a comprehensive process-monitoring platform specifically designed for microalgae R&D. The physicochemical variables, optical density, dry weight and chlorophyll fluorescence parameters, as well as the environmental parameters, pH, temperature, light intensity and CO2 concentration, were detected online at 20-minute intervals. The L. zhangjiangensis biomass concentration increased by 17% under the pH-steady mode compared to the CO2 steady mode, whereas there was no difference in the N. oceanica biomass concentration. By using Algal Station, a notable difference was also found in the periodical change of F-v/F(m)between these two strains. This is the first systematic study of F-v/F-m variation during light and dark cycles in microalgae. The results obtained by Algal Station are important for basic physiological studies and dynamic process optimizations for more efficient microalgae cultivation.