Lignocellulosic bioethanol is a promising renewable energy source that can reduce greenhouse gas emissions and improve energy security. However, its commercialization faces significant economic and environmental challenges, including high feedstock costs, complex pretreatment processes, expensive enzyme formulations, and substantial energy and water requirements. This review examines the key factors affecting its viability, including feedstock costs, enzyme efficiency, co-product generation, greenhouse gas emissions, water use, energy efficiency, and land use impacts. Recent advancements in pretreatment technologies, enzyme recycling, genetically engineered microbial strains, and fermentation strategies are discussed for their potential to improve process efficiency and reduce production costs. This review also explores co-product valorization, including lignin and biogas utilization, which can enhance the economic sustainability of bioethanol production by generating additional revenue streams, offsetting operational costs, and improving overall process efficiency. Identifying research gaps, it highlights the need for cost-effective feedstock supply chains, advanced enzyme technologies, and optimized fermentation methods. Additionally, the role of life cycle assessments and government policies, including subsidies, is considered in shaping production costs and the environmental impact. By integrating economic and environmental perspectives, this review provides insights into advancing the sustainable production of lignocellulosic bioethanol, emphasizing the importance of continued innovation to overcome existing challenges.

In the current study, alkaline hydrogen peroxide pretreated oil palm trunk fibers were subjected to ethanol production via simultaneous saccharification and fermentation (SSF). The effect of high substrate loading, enzyme and substrate feeding strategy, and influence of a pre-hydrolysis step in SSF was studied to scale up ethanol production. In the enzyme feeding strategy, the addition of an enzyme at the start of fed-batch SSF significantly (p < 0.05) increased ethanol concentration to 51.05 g/L, ethanol productivity (Q_P) to 0.61 g/L·h, and ethanol yield (Y_P/S) to 0.31 g/g, with a theoretical ethanol yield of 60.65%. Furthermore, the initial velocity of the enzyme (V₀) in the first 8 h was 2.27 (g/h) with a glucose concentration of 18.17 g/L. On the other hand, the substrate feeding strategy and pre-hydrolysis simultaneous saccharification and fermentation (PSSF) process were studied in a 1 L fermenter. PSSF in fed batch with 10 and 20% (w/v) significantly improved enzyme hydrolysis, circumvent the problems of high viscosity, reduced overall fermentation time, and gave the highest ethanol concentration of 51.66 g/L, ethanol productivity (Q_P) of 0.72 g/L·h, ethanol yield (Y_P/S) of 0.31 g/g, and theoretical ethanol yield of 60.66%. In addition, PSSF with 10 and 20% significantly increased the initial velocity of the enzyme (V₀) to 4.64 and 4.40 (g/h) and glucose concentration to 37.14 and 35.27 g/L, respectively. This result indicated that ethanol production by PSSF along with substrate feeding could enhance ethanol production efficiently.