Zero-carbon solution: Microalgae as a low-cost feedstock for fuel production and carbon sequestration

The increasing environmental issues, driven by the depletion of fossil fuel reserves and excessive carbon emissions, have put the world's attention toward finding sustainable solutions. Among various solutions, microalgae emerge as a promising zero-carbon alternative, addressing both biofuel production and carbon sequestration. This review provides a comprehensive analysis of cultivation methods for microalgae, biofuel conversion techniques (bioethanol and biodiesel), and their role in reducing/eliminating greenhouse gas (GHGs) emissions. Recent developments in cultivation methods, such as photobioreactors and open-pond cultivation have shown encouraging results regarding the CO2-capturing potential of microalgae. Specific microalgal strains, such as Chlorella vulgaris and Chlorella sp. exhibit high biomass productivity (0.4 and 1.21 g/L/d, respectively) and CO2 fixation rates (0.49 and 0.25 g/L/d, respectively), standing out as the most viable for biofuel synthesis. Additionally, this review compares various cultivation systems based on techno-economic analysis (TEA) with an aim to highlight cost-effective and industrially feasible systems. Among the analyzed strains, Nannochloropsis oceanica outperformed the other strains in terms of biodiesel productivity (0.36 g/L/d), production costs ($1.5/L), and EROI (13.5). This makes it an excellent choice for large-scale biofuel production. By integrating biofuel production and CO2 sequestration, this review identifies key challenges and future research directions for economically feasible microalgal bioenergy solutions.