Synergistic acid–sodium bisulfite pretreatment of banana straw for enhancing cellulose utilization: A comprehensive physicochemical and multivariate mechanism analysis

Banana straw (BS), a lignocellulosic residue abundant in tropical regions, represents a valuable resource for sustainable agricultural development when efficiently processed. Acid–sodium bisulfite pretreatment (ABP) was investigated for its impact on BS cellulose utilization. Response surface methodology with Box–Behnken design optimized ABP parameters to 150 °C, 1% H2SO4 (w/v), 12% NaHSO3 (w/w), 40 min, and solid-to-liquid ratio of 1:12. Compared with the sole sulfuric acid pretreatment (SSAP), the optimized ABP improved enzymatic hydrolysis, yielding 1.35-fold higher conversion rate of cellulose (CRC) and 1.37-fold greater yield of reducing sugars (YRS). Comprehensive analyses of the structural, physicochemical, and cellulose crystalline properties of BS elucidated the mechanisms underlying hemicellulose/lignin removal and cellulose exposure during pretreatment. Multivariate correlation analysis of 17 variables revealed relatively positive associations between enzymatic efficiency and cellulose recovery rate (CR), crystallinity index of cellulose (CrI), Congo red dye adsorption (CR ads.), and sulfonic acid content (SAC) (|r| > 0.8). NaHSO3 concentration showed positive associations with lignin removal rate (LR), SAC and CR ads., and corresponded to a decreased C/O ratio. Temperature was positively associated with hemicellulose removal rate (HR) and YRS, though temperatures above 150 °C were linked to reduced LR. H2SO4 concentration showed an association with HR but exhibited limited relationship with enzymatic hydrolysis efficiency. These observed trends suggest that ABP could serve as an effective strategy for enhancing lignocellulosic biomass utilization from agricultural residues, though given the relative sample size, these correlations should be interpreted as indicative of associations rather than definitive causal relationships.

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