Integrated KOH-SDS-microwave pretreatment for enhanced delignification of agro-waste biomass for second-generation biorefinery applications.

Lignocellulose biomass is the most abundant renewable feedstock on Earth, composed of polymers (both sugar and aromatic) and thus a highly sustainable resource for developing value-added products. The naturally present biomass is highly complex and tough due to the formation of a lignin-carbohydrate matrix, making it more recalcitrant. Therefore, a pretreatment is necessary to remove lignin and enhance the enzyme accessibility. Depending on the type of biomass, a specific pretreatment approach was selected. It is well known that combining two or more different pretreatment strategies effectively reduces complexity. In the present study, an integrated approach was used in which 1% KOH and 0.5% SDS, along with different microwave power levels (100W to 450W), were combined to pretreat Pisum sativum pods and Eichhornia crassipes agro-waste for effective delignification. The characterization study resulted in delignification up to ≈ 93% in WH and ≈ 97% in PP at a power level of 450W. Although XRD, FTIR, and FE-SEM results showed an increased crystallinity index, consistent cellulose peaks, and increased cracks and a rougher surface in both biomass samples with increasing power levels, suggesting the effectiveness of the pretreatment. The cellulose component recovery in WH ranged from 98.80 to 79.25% (w/w), and in PP, it ranged from 95.02 to 56.08% (w/w), and both were correlated with estimates of total reducing sugars released in the slurry. Overall, this study demonstrates an integrated physicochemical approach, establishing a highly efficient and reproducible pretreatment route for removing amorphous regions from a variety of biomasses.