Enhancing microalgal productivity through bioactive substances, light, and CO2.

Microalgae play a crucial role in ecosystems, from oxygen production to sustaining food webs and offering valuable applications in industry and environmental management. Increasing their productivity in terms of biomass yield, cultivation time, and nutritional or metabolite quality remains a major challenge. This study assessed the effects of 10 bioactive substances (including lactones, phytohormones, and natural extracts), four light wavelengths, and four CO₂ injection regimes on Arthrospira platensis, Chlorella vulgaris, Ankistrodesmus falcatus, and Tetradesmus dimorphus, using linear modeling and LSD (Least Significant Difference) post hoc tests. N-butyryl-DL-homoserine lactone significantly enhanced A. platensis growth (94.4%), while naphthaleneacetic acid and indole-3-butyric acid promoted T. dimorphus growth (138.1% and 115.5%, respectively). More accessible alternatives, such as Aloe vera and coconut water, also stimulated growth: A. platensis, C. vulgaris, and A. falcatus increased by 85.3%, 69.2%, and 87.7% with Aloe vera, while T. dimorphus increased 80.5% with coconut water. Regarding light quality, red light (600-700 nm) benefited A. platensis and A. falcatus (49.2% and 20.8%, respectively), whereas blue light (400-490 nm) favored C. vulgaris and T. dimorphus (57.7% and 31.5%, respectively). CO₂ injection further enhanced biomass production and carbon fixation, particularly in C. vulgaris and A. falcatus (73.5% and 53.5%, respectively). However, combined treatments did not produce additive effects, suggesting complex interactions. Overall, these findings demonstrate the potential of bioactive substances and environmental conditions to improve microalgal performance and highlight the importance of investigating synergistic effects and scalability for large-scale production.