Optimization of dry chemomechanical and deep eutectic solvent pretreatment of mango peel biomass for enhanced lignin removal

Abstract

The recalcitrant nature of lignocellulosic biomass presents a significant challenge for lignin removal, a critical step for its effective utilization. This study optimized an integrated dry chemomechanical-assisted deep eutectic solvent (DES) pretreatment process to maximize delignification in mango peel waste. By utilizing a Box-Behnken Design (BBD) alongside Response Surface Methodology (RSM), the study evaluated four key parameters: milling time (20-60 min), NaOH concentration (1-3% w/w), rotational speed (200-300 rpm), and solid-to-liquid ratio (1:10-1:20 g/mL). Findings indicated that optimal conditions 3% NaOH, 40 min of milling at 250 rpm, and a 1:15 g/mL ratio yielded a theoretical lignin removal efficiency of 88.10%. Experimental validation under these parameters achieved an actual removal rate of 88.10%, confirming the high predictive accuracy of the model. SEM analysis revealed severe surface disruption after pretreatment, while FTIR confirmed substantial reduction of lignin-associated aromatic functional groups. XRD analysis showed that the crystallinity index increased from 12.2% in raw mango peel to 55.5% after pretreatment, confirming effective removal of amorphous lignin and hemicellulose fractions. These results demonstrate that the dry chemomechanical-DES approach is a highly efficient, sustainable, and green pretreatment strategy for repurposing agricultural waste. By streamlining the flow and enhancing the technical precision, this version highlights the study's robust methodology and its environmental significance.