Microalgae for sustainable energy: Techno-economic and life cycle insights into biodiesel and biohydrogen production

• Microalgae pathways assessed for biodiesel and RFV-based biohydrogen production. • Biodiesel shows 78% CO 2 reduction and net negative global warming potential. • RFV biohydrogen delivers higher NPV but faces capital and catalyst challenges. • Comparative TEA–LCA reveals trade-offs between near- and long-term viability. • Bangladesh conditions favor low-cost algal cultivation and biorefinery integration. This study explores the potential of microalgae as a renewable energy source, with a focus on producing biodiesel and biohydrogen as sustainable alternatives to fossil fuels. Microalgae are particularly attractive because of their high productivity, ability to capture carbon, and adaptability to local aquatic environments. Two conversion routes are examined: biodiesel production through transesterification and biohydrogen generation via reactive flash volatilization (RFV). A techno-economic and life cycle analysis is used to compare their performance in terms of energy output, costs, and environmental impact. The results show that biodiesel yields are high, reducing CO 2 emissions by 78% and achieving a net negative global warming potential, but remain energy-intensive and less profitable, with a net present value (NPV) of 229 million USD. In contrast, RFV-based biohydrogen demonstrates a stronger energy balance and higher economic potential (NPV: 624 million USD), although it requires a longer payback period. Both pathways face challenges, but biodiesel emerges as the most viable near-term solution, while biohydrogen from RFV offers superior long-term returns, considering current technical and economic barriers. Overall, the study highlights that with policy support, integrated biorefineries, and further research, microalgae-based fuels could play a meaningful role in advancing energy security and achieving long-term sustainability goals.