The Influence of Elevated CO2 Concentrations on the Growth of Various Microalgae Strains

The influence of elevated CO2 concentrations on the growth and viability of various microalgae strains was studied. Arthrospira platensis, Chlorella ellipsoidea, Chlorella vulgaris, Gloeotila pulchra, and Elliptochloris subsphaerica were tested. The cultivation of microalgae was carried out at constant CO2 concentrations (0.04, 3, 6, or 9%—sequentially from lower to higher concentrations), under constant (24 h·day−1) illumination with an intensity of 74.3 µmol quanta·m−2·s−1, and a constant temperature of 23.5 ± 0.5 °C. The optical density of the microalgae biomass, pH, and the chemical composition of the culture medium were measured. Microscopy (including the cytochemical microscopic method) was conducted to monitor the state of the microalgae. The highest biomass growth rate (0.37 g·L−1·day−1), among all experiments, was achieved for Chlorella vulgaris at CO2 = 3% and for Chlorella ellipsoidea at CO2 = 6 and 9%. The lowest growth rate (0.12 g·L−1·day−1) was achieved for Arthrospira platensis at CO2 = 3 and 9%. The microscopy results showed the absence or a minimum number of dead cells of the strains under selected conditions. The ability to maintain the viability of cultures up to significant concentrations of CO2 = 9% was due to adaptation (gradual increase in CO2 concentrations in the experiments). © 2023 by the authors.