Bioethanol revolution: Integrating feedstock innovation with energy-efficient processes under life cycle assessment

The global energy system remains heavily dependent on fossil fuels, increasing the need for renewable liquid alternatives. Bioethanol is a major gasoline substitute that can reduce petroleum use in transport by 5–27% under typical blending mandates (E10–E27) and up to 100% on an energy basis in neat ethanol applications (E100). However, first-generation production from food crops raises economic and food–fuel concerns. This review summarizes recent advances in second- and third-generation bioethanol from lignocellulosic biomass, agricultural and industrial residues, and microalgae, with emphasis on process intensification and sustainability performance. A comparative life-cycle assessment (LCA) and techno-economic analysis evaluate pathways based on net energy ratio, life-cycle GHG emissions, and production cost. Lignocellulosic ethanol can achieve 40–91% GHG reductions relative to gasoline, though costs remain variable (∼ 0.21–1.25 USD/L). Mature sugar/starch routes show competitive costs (∼ 0.34–0.47 USD/L) with significant carbon benefits when land-use change is minimized. Waste/residue pathways emerge as the most robust near-term option, while microalgae-based ethanol remains limited by energy and cost constraints (NER <1; ∼ 0.76– 0.91 USD/L). Overall, this review identifies the most viable deployment routes and key research priorities for advancing low-carbon bioethanol systems.