Effects of Light Intensity on the Growth and Biochemical Composition in Various Microalgae Grown at High CO₂ Concentrations

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: <i>Arthrospira platensis</i>, <i>Chlorella ellipsoidea</i>, <i>Chlorella vulgaris</i>, <i>Gloeotila pulchra</i>, and <i>Elliptochloris subsphaerica</i>. 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 <i>C. vulgaris</i> (0.78 g·L⁻¹·d⁻¹) at an illumination intensity of 245 µmol quanta·m⁻²·s⁻¹. For <i>E. subsphaerica</i> and <i>A. platensis</i>, 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 <i>C. vulgaris</i> (from 61.0 to 46.6%) and <i>A. platensis</i> (from 43.8 to 33.6%), and a slight increase in lipid content was shown by <i>A. platensis</i> (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.