Enhanced high-solids hydrolysis of pretreated wheat straw at low enzyme dosage via dual mechanisms of lignin surface passivation and aqueous environment modulation.

The enzymatic hydrolysis of lignocellulosic biomass under high-solid loading is hindered by inefficient mass transfer and high enzyme dosage. In this study, two polymeric additives, polyvinyl alcohol (PVA) and polyethylene glycol 4000 (PEG4000), were employed to enhance the saccharification of dilute-acid pretreated wheat straw (PWS) under high-solid loading (15% w/w) and low enzyme dosage (2.7 FPU/g dry substrate). Using a multi-scale characterization approach, these PVA and PEG4000 were found to overcome different hydrolysis barriers through distinct mechanisms. PVA primarily acts through competitive blocking of lignin surfaces, reducing non-productive enzyme adsorption by 60.02%. In contrast, PEG4000 modifies the aqueous microenvironment through entropy-driven interactions, dispersing enzyme aggregates and liberating constrained water, which reduces system viscosity by 88.5%. The cellulose conversion of PWS increased from 58.2% to 81.3% with PVA and to 70.3% with PEG4000 addition. The structure-function understanding of polymeric additives provides a rational framework for additive selection: PVA proves most effective in systems dominated by non-productive adsorption, while PEG4000 excels where mass transfer limitations prevail. This work establishes a strategic basis for optimizing polymeric additives in industrial lignocellulose bioprocessing.