Pretreatment Approach And Efficiency Of Plant Biomass For Fermentable Sugar Production

In the production of biofuel from biomass,the enzymatic hydrolysis potential?EHP?of feedstock plays a critical role in determining the enzymatic saccharification efficiency?ESE?and economic feasibility.Meanwhile,the cost-effective pretreatment technologies play an important role in meeting the world's demand for bioenergy.In this study,the simulative biomass of Eichhornia crassipes?EC?and sugarcane bagasse?SB?,as well as the actual biomass of EC and SB pretreated by 4 different chemical methods,were subjected to enzymatic hydrolysis.A binary linear-regression equation?BLE?,y=?₁?₁+?₂?₂,was derived to illustrate the relationship between the sugar yield?y?and the proportions of key components?cellulose and hemicellulose???₁,?₂?with different compositional contributions??₁ and?₂?to y.Additionally,EC,SB and Metasequoia glyptostroboides?MG,as a control material?were used as enzyme substrates to explore the influences of Fenton?FT?and peroxyacetic acid?PAA?pretreatments,as well as EC harvest period on the fermentable sugar production,through changes to available biomass,chemical compositions and structural characteristics.Furthermore,the impacts of Fe²⁺and H₂O₂ input,as well as plant particle size on the adsorbability of Fe²⁺on substrate and the oxidation efficiency of hydroxyl radical?·OH?were investigated in the process of pretreating plant biomass by FT.The main results are summarized as following:1.A simple and economical model was constructed to inform decisions on the EHP of different types of plant biomass.In the enzymatic hydrolysis process,EC cellulose was found to make greater contributions than SB cellulose to fermentable sugar production,resulting in higher ESE of EC than SB.This comparative model advances the understanding of roles played by key biomass components in the enzymatic hydrolysis process.Furthermore,the ESE of pretreated actual biomasses exhibited similar trends and positive correlation with the predictions,indicating good applicability of the BLE model and highlighting the superior EHP of EC than SB.2.The suitable pretreatment methods were matched for different plant biomass by characterizing the effects of pretreatment severity on recalcitrance of substrate.The optimal pretreatments for the EC,SB and MG biomass were FT,PAA,and PAA,respectively.Overall,FT exhibited a higher ability to remove lignin from EC and increase the EC carbohydrate contents?from 67.48%to 86.57%?,while PAA performed better in lignin removal from SB and MG,and increasing carbohydrate contents of SB?from68.83%to 90.63%?and MG?from 71.96%to 93.73%?.Furthermore,following their respective optimal pretreatments,the cell surfaces of each plant type were observably compromised,with distinct increases to the specific surface area,inner porosity,and enhanced substrate crystallinity,thus entailing significantly improved carbohydrate accessibility to enzymes.The results ultimately indicated that FT pretreatment was more appropriate for plant biomass with lower lignin content and lower crystallinity index?CrI?,while PAA pretreatment was more suitable for plant biomass with higher lignin content and higher CrI.3.The structure-activity relationship of enzymatic hydrolysis of FT-EC was determined to provide a feasible scheme for bioconversion of plant biomass.The ESE of raw EC materials were generally very low?<10.36%?and increased considerably after FT pretreatment?form 26.98%to 62.24%?.As the harvest time extended,the lignin content of the raw EC biomass increased while the CrI decreased.The reversal trends were observed for these two factors after FT pretreatment.Generally,both factors are negatively correlated with enzymatic hydrolysability of EC.The CrI is likely to be the most important factor that determines the enzymatic hydrolysability of EC,while lignin content affects it secondly.Considering the benefits of available biomass and bioconversion efficiency,the mature EC samples were more suitable for fermentable sugar production,given their ESE at 72h was 41.27%,and reducing sugar yield was 8.81g/plant following FT pretreatment.4.The reaction process of·OH^Fe²⁺synergistic pretreatment system was analysed to clarify the mechanism of efficient bioconversion of plant biomass through Fenton reagent formula combined with substrate particle size.The generation efficiency of·OH could be considerably improved by regulating the Fe²⁺and H₂O₂ input.Both of the generation rates and yields of·OH were highly positive correlated with the removals of lignin?R²=0.9782 and R²=0.9259,respectively?,whereas showed no significant relationships with those of cellulose and hemicellulose.Moreover,the rapid increase of·OH resulted in a distinct weakening to the structural signal of benzene ring in lignin,thus revealing that·OH selectively degraded the components of plant biomass and exhibited high specificity for the oxidative degradation of lignin due to the benzene ring structure.This triggered the damage of cell surface structure,thus enhancing the ESE of EC.Furthermore,the surface adsorption properties of ECs increased with their decreasing particle sizes,which was beneficial to the enrichment of Fe²⁺on their surfaces.After FT pretreatment,the percentage of Fe elements on the surface of EC with minimum particle size increased remarkably?from 0.46%to21.54%?,inducing the FT reaction?liquid phase?to focus on the substrate surface?solid phase?,thus significantly improving the effectiveness of·OH on the oxidative degradation of lignin.With the help of this favorable condition,the lignin removal reached 96.19%,the cell surface was reconstructed,and the surface adsorption performance further increased drastically.Moreover,the crystalline structure was transformed from cellulose I to cellulose II,which greatly enhanced the enzyme accessibility and enzyme degradability of carbohydrates.After optimal FT pretreatment,the ESE of EC at 48h reached 92.08%,in which the conversion of glucose and xylose were 96.04%and 87.01%,respectively.