Valorization of Agro-Industrial Residues for Bioethanol: A Comparative Review of Brewer’s Spent Grain, Cassava, and Yam Peels

Onuora Okorie

Abstract

Escalating global energy demand and the environmental consequences of fossil fuel dependence have intensified the urgent imperative for sustainable renewable energy sources. Bioethanol derived from lignocellulosic biomass represents a promising and strategic alternative. This critical, comparative review provides an original synthesis of the valorization pathways for three high-impact agro-industrial residues—yam peels, cassava peels, and brewer’s spent grain (BSG)—for advanced bioethanol production, focusing on the interplay between feedstock composition, rigorous pretreatment, and bioprocess optimization. Crucially, the analysis establishes an original analytical framework demonstrating that the significant variability in reported ethanol yields is directly correlated with the inherent heterogeneity in the proximate and chemical composition of the feedstocks, compounded by disparities in pretreatment methodologies and saccharification protocols. Pretreatment plays an indispensable role in overcoming lignocellulosic recalcitrance, thereby enhancing the enzymatic hydrolyzability of structural polysaccharides. The comparative assessment identifies BSG as the superior fermentation substrate, exhibiting high carbohydrate and low inhibitory compound profiles, with documented ethanol yields approaching 94% in optimized processes. Current research trends mandate the adoption of advanced statistical optimization and kinetic modeling techniques for enhancing conversion kinetics, reducing operational costs, and improving the techno-economic feasibility. This waste-to-energy paradigm directly contributes to a circular bioeconomy by converting low-value waste streams into high-value biofuel, thereby addressing challenges in waste management and climate change mitigation. The review concludes by delineating critical future research trajectories in strain engineering and AI-driven bioprocess modeling to realize the full, sustainable potential of 2G bioethanol production.

Keywords

Bioethanol, lignocellulosic biomass, circular bioeconomy, pretreatment methods, fermentation, bioprocess modeling.

Corresponding Author

Onuora Okorie, Department of Chemical Engineering, Enugu State University of Science and Technology, Enugu, Nigeria.

Citation

Okorie, O. (2025). Valorization of Agro-Industrial Residues for Bioethanol: A Comparative Review of Brewer’s Spent Grain, Cassava, and Yam Peels. Res Next Gen Mater Eng, 1(1), 01-37.