RESUMO
In modern energy, various technologies for absorbing carbon dioxide from the atmosphere are being considered, including photosynthetic microalgae. An important task is to obtain maximum productivity at high concentrations of CO2 in gas-air mixtures. In this regard, the aim of the investigation is to study the effect of light intensity on the biomass growth and biochemical composition of five different microalgae strains: Arthrospira platensis, Chlorella ellipsoidea, Chlorella vulgaris, Gloeotila pulchra, and Elliptochloris subsphaerica. To assess the viability of microalgae cells, the method of cytochemical staining with methylene blue, which enables identifying dead cells during microscopy, was used. The microalgae were cultivated at 6% CO2 and five different intensities: 80, 120, 160, 200, and 245 µmol quanta·m-2·s-1. The maximum growth rate among all strains was obtained for C. vulgaris (0.78 g·L-1·d-1) at an illumination intensity of 245 µmol quanta·m-2·s-1. For E. subsphaerica and A. platensis, similar results (approximately 0.59 and 0.25 g·L-1·d-1 for each strain) were obtained at an illumination intensity of 160 and 245 µmol quanta·m-2·s-1. A decrease in protein content with an increase in illumination was noted for C. vulgaris (from 61.0 to 46.6%) and A. platensis (from 43.8 to 33.6%), and a slight increase in lipid content was shown by A. platensis (from 17.8 to 21.4%). The possibility of increasing microalgae biomass productivity by increasing illumination has been demonstrated. This result can also be considered as showing potential for enhanced lipid microalgae production for biodiesel applications.
RESUMO
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).
