Two-stage cultivation of the microalga Chlorella fusca LEB 111 using the phytohormone indole-3-acetic acid and nitrogen reduction for assessment of aviation fuel applications

Microalgae can produce neutral and polar lipids, which are of great interest for biofuel production. However, two-stage cultivation presents a promising strategy to overcome this challenge. This study evaluated the influence of supplementation with the phytohormone indole-3-acetic acid (IAA) and nitrogen reduction in the two-stage cultivation of the microalga Chlorella fusca LEB 111, focusing on increasing biomass and lipid content. In the first stage, IAA was added at different times (0, 5, and 10 d) and concentrations (0.01 and 0.1 mg L −1 ). Subsequently, the second stage was conducted with nitrogen concentration reductions (50%, 75%, and 87.5%). After cultivation, oil was extracted from the microalgal biomass and characterized by FTIR, NMR, TGA, and fatty acid profile. The supplementation of 0.01 mg L −1 IAA on day 0 combined with an 87.5% nitrogen reduction resulted in the highest lipid content and final biomass productivity (37.3% and 42.0 mg L −1 d −1 ) as well as a 67% reduction in lipid production costs. This condition resulted in a 61% mass loss in the TGA, indicating a high macromolecule content. FTIR peaks at 3000–3100 cm −1 confirmed hydrocarbons and 1 H NMR signals at 4.10–4.31 ppm indicated triacylglycerols. The fatty acid profile, comprising 50.2% saturated fatty acids, underscores the potential of the biomass for biojet fuel production. Finally, the oil obtained from the biomass produced with IAA supplementation and nitrogen reduction shows potential for application in aviation biofuels, aligning with the sector's future perspectives by expanding the supply of sustainable feedstocks and contributing to the reduction of greenhouse gas emissions.