Characterization Of The Wall Polymer Features That Affect Biomass Saccharification And Ethanol Production In Miscanthus

Bioenergy is considered as a renewable and sustainable energy derived from biological sources. As the second generation of bioenergy, lignocellulosic biomass conversion into bioethanol involves three major steps: pretreatment, enzymatic digestion and fermentation. Howeve, recalcitrance of plant cell wall makes the current biomass process unacceptably expensive. Because lignocellulosic biomass is derived primarily from plant cell walls composed of cellulose, hemicelluloses, and lignin, it becomes essential to explore the major factors of plant cell wall that affect biomass saccharification and sugar-ethanol conversion rate.In this study, supernatants from pretreatments of Miscanthus biomass were obtained to detect the byproducts that inhibit yeast fermentation for ethanol production. Among the byproducts, ferulic acid and p-comaric acid were produced mainly from the alkali pretreatment, while furfural and 5-hydroxymethylfurfural(5-HMF) were from the acid pretreatment. The results suggested that the alkali pretreatment caused lignin degradation and acid pretreatment affected sugar degradation. With regard to yeast fermentation of the supernatants from pretreatments, hemicelluloses and lignin content in the raw materials had positive and negative effects on sugar-ethanol conversion rate, respectively. Correlation analysis showed that the byproduct extracted from alkali pretreatment, such as vanillin and syringic acid, exhibited negative effect on ethanol production, whereas 5-HMF was positively correlated with ethanol conversion. Furthermore, sugar-ethanol conversion rate decreased significantly by adding the phenolic byproduct, and increased by supplying furfural compound. Accumalutive effect was not observed by adding multiple byproducts. Notably, phenolic inhibiton of yeast fermentation was lessened by adding furfural.Meanwhile, one- and two-step pretreatments with alkali and acid were performed in three Miscanthus species that exhibit distinct hemicelluloses levels. Among various pretreatments, one-step with 4% Na OH or two-step with 2% Na OH followed by 1% H2SO4 was found to be optimal for high biomass saccharification, indicating that alkali was the main effecter of pretreatments. Notably, both one- and two-step pretreatments largely enhanced biomass digestibility distinctive in hemicelluloses-rich samples by effectively co-extracting hemicelluloses and lignin. Semi-simultaneous saccharification and fermentation(semi-SSF) followed by high solid pretreatment exhibited the same impact of hemicelluloses on ethanol yields. However, correlation analysis further indicated that the effective lignin extraction, other than the hemicelluloses removals, predominately determined biomass saccharification under various alkali and acid pretreatments, leading to a significant alteration of cellulose crystallinity.Hence, this study suggestes the potential approaches in bioenergy crop breeding and bioethanol process technology.