Synergistic Sustainable Biorefinery Approach for Corncob Biomass: Optimization, Production, and Assessment of Bioethanol, Glycerol, and Xylooligosaccharides

Abstract

This study investigates the prospect of tailored biorefinery objectives targeting specific anatomical sections of corncobs, an underexplored area in the field. The corncob is dissected into its rigid outer anatomical portion (CO) and its inner soft pith (CP). Initially, the comprehensive biomass composition of both CO and CP was determined through four different methods. CP exhibited a higher carbohydrate content and lower lignin content (83.32% and 13.58%, respectively) compared to CO (79.93% and 17.12%, respectively). The syringyl/guaiacyl (S/G) ratio was higher in CP (1.34) than in CO (1.28). Physical characterization confirmed lower crystallinity and thermal stability in CP compared to CO. Saccharification yield of CP without pretreatment matched that of pure cellulose and xylan controls. Subsequently, sustainable pretreatment methodologies for CO were optimized using central composite design. Results were validated using hybrid-artificial neural network models incorporating metaheuristic optimization of hyperparameters through Teaching-Learning-Based Optimization (TLBO), Particle Swarm Optimization (PSO), and Genetic Algorithm (GA). Three potential pretreatment methodologies—NaHCO3, NaOH, and sequential treatment (NaOH followed by H2SO4)—were identified, yielding pretreated CO residues COr1, COr2, and COr3 respectively. A novel strain of Pichia kudriavzevii was isolated from ripened Palmyra palm (Borassus flabellifer) fruit pulp, exhibiting high tolerance to ethanol, lignocellulose-derived inhibitors, and fermentation of various carbon sources (including xylan) over a pH range of 2.5 to 8.5. Simultaneous saccharification and co-fermentation (SSCF) and separate hydrolysis and fermentation (SHCF) modes were employed to valorise COr1, COr2, and COr3 individually. Achieved ethanol and glycerol concentrations 63%, 5% of their theoretical yield (T.Y) respectively. The techno-economic analysis revealed an overall negative profit margin. However, this disparity is notably narrower for the NaOH pretreatment scenario (USD 18.0). This gap can be readily surmounted, when factoring in the co-product credit from the revenue generated (USD 203.3) through XOS production from CP. The potential of xylooligosaccharides production from CP was demonstrated by saccharifying untreated CP with commercial xylanase, achieving an impressive yield of 77% of its theoretical yield (T.Y.). Among the evaluated scenarios, the SSCF process utilizing COr2 in conjunction with XOS production from CP emerged as the most economically sustainable biorefinery option. Although NaOH pretreatment shows lower exergy performance metrics (process efficiency 0.91, sustainability index 10.90, and environmental vi impact 0.09) compared to sequential H2SO4 pretreatment, its economic viability and sustainability make it the preferred choice.