A comprehensive review of seaweed macroalgae as a biodiesel feedstock for transportation fuel in diesel engines

The world faces growing demand for renewable transportation fuels due to limited crude oil reserves and environmental degradation. The review comprehensively examines biodiesel feedstocks using criteria for technology readiness, sustainability, and life cycle assessment (LCA). First-generation (G1) feedstocks face food-versus-fuel competition, low productivity, and high land use requirements. Second-generation (G2) feedstocks having problems of limited farmland and processing efficiency. In contrast, third-generation (G3) marine macroalgae (containing ˃5% lipids) exhibit higher biomass productivity (7–30 times land crops), grow rapidly, and are well-suited to existing aquaculture facilities. Key advancements, challenges, and pathways for producing macroalgae-based biodiesel are critically examined. The diesel engine performance and emission characteristics of biodiesel blends (B10–B20) from macroalgae show a good balance between brake thermal efficiency (BTE) and brake-specific fuel consumption (BSFC) and reductions in CO, HC, PM, and smoke emissions, with a slight increase in CO2 and NOx. The efficiency and scalability of oil/lipid extraction through Soxhlet, pyrolysis, and hydrothermal liquefaction (HTL), are compared. This review provides a quantitative assessment that connects feedstock productivity, conversion pathways, engine performance, by LCA, techno-economic indicators, and industrial biorefinery integration, unlike previous reviews.Overall, seaweed macroalgae represent promising sustainable biodiesel feedstocks , particularly with process integration, co-product valorization, and energy-efficient technologies.