Experimental, Technoeconomic, and Life-Cycle Evaluation of One-pot Biomass Pretreatment for Ethanol Production

Brewer’s spent grain (BSG), a byproduct rich in carbohydrates, presents a promising feedstock for cellulosic ethanol production. This study focused on the technoeconomic analysis (TEA) and life cycle assessment (LCA) of ethanol production, considering various combinations of BSG solid loadings (10-30% w/v) and enzyme dosages (10-30 FPU/g BSG). A one-pot CaO pretreatment followed by pH adjustment with H ₃PO ₄ and simultaneous saccharification and fermentation (SSF) with engineered yeast were employed. As the solid loading increased, the ethanol concentration rose from 16.4 to 39.3 g/L, while the ethanol yields decreased. For instance, with an enzyme dosage of 30 FPU/g BSG, the ethanol yield dropped from 18.8 to 11.1 g ethanol/100 g BSG. Notably, increasing the enzyme dosage significantly improved ethanol concentration by 3.4-6.8 g/L and yield by 2.0-3.2 g ethanol/100 g BSG. The TEA results revealed that the lowest minimum ethanol selling price (MESP) of $3.9/kg was achieved at a 20% solid loading and an enzyme dosage of 10 FPU/g BSG (S20E10). The sensitivity analysis of MESP highlighted the key economic drivers, including enzyme costs, plant capacity, and BSG glucan content. The LCA results indicated that enzyme use is the primary contributor to greenhouse gas emissions (GWP), ranging from 2.7 to 11.3 kg CO ₂eq/kg ethanol, when biogenic emissions are excluded. For S20E10, the LCA selectivity analysis showed that enzyme use causes GWP to fluctuate between 4.4 and 7.8 kg CO ₂eq/kg ethanol, while H ₃PO ₄ contributes 1.0-1.6 kg CO ₂eq/kg. These findings emphasize the importance of balancing enzyme use and process efficiency rather than solely maximizing yield in achieving cost-effectiveness and environmental sustainability for cellulosic ethanol production.