Optimization of pre-commercial enzyme dosage for a potential lignocellulosic biorefinery

Abstract

Lignocellulolytic enzymes remain one of the primary cost constraints in secondgeneration (2G) ethanol biorefineries. Achieving efficient hydrolysis of structural carbohydrates with minimal enzyme dosage, maintaining slurry fermentability for industrially relevant ethanol titers, and maximizing ethanol yield per ton of biomass are among the major challenges in 2G processes. In this study, we optimized the dosages of pre-commercial cellulase (NS22257) and hemicellulase (NS22244) on pilot-scale, hydrothermally pretreated lignocellulosic substrates.Enzyme dosages were evaluated at three levels: 20 mg cellulase with 7.25 mg hemicellulase (ED-1), 40 mg with 14.5 mg (ED-2), and 60 mg with 21.75 mg (ED-3). As expected, the highest sugar yields were obtained with ED-3; however, for sweet sorghum, oilcane, and miscanthus, sugar yields from ED-2 and ED-3 were not significantly different (p < 0.05). For example, sweet sorghum produced 123.78±1.54 g/L and 125.76±0.46 g/L of total sugars (glucose and xylose) with ED-2 and ED-3, respectively. Although energycane exhibited statistically significant difference between ED-2 and ED-3, the incremental grain with ED-3 was modest, increasing sugar release by only 9.02 g/L relative to ED-2. Importantly, ED-1 resulted in sugar yields of 88.88±3.64 to 106.86±1.21 g/L, sufficient to achieve ethanol titers ≥40 g/L, the threshold required for industrial relevance. A semi-integrated bioprocess validated this outcome, producing 42.09±2.38 g/L ethanol and an estimated yield of 213.38 L of ethanol per dry ton of pretreated biomass, requiring only 20.83 L of cellulase and 6.25 L of hemicellulase per ton. Remarkably, these enzyme dosages are approximately tenfold lower than those reported in prior studies.