Salt-frost pretreatment disrupts the dense structure of poplar coupled with hydrothermal processing to enhance enzymatic hydrolysis

The dense structure of woody biomass leads to high-intensity pretreatment methods involving acids, alkalines, chemical reagents, or significant energy inputs. However, the fundamental causes of this phenomenon have not been correlated. This study investigates the application of salt-frost, a natural energy source, in combination with hydrothermal treatment to enhance enzymatic hydrolysis of poplar and to explore the correlation between the dense structure and the treatment intensity. Salt-frost pretreatment enhances poplar's porosity and substrate flowability, reducing water saturation by 5.2–10.1 % compared to untreated samples. Salt-frost reduces hydrothermal severity by 84.0 %, significantly reducing levels of formic acid, 5-hydroxymethylfurfural, and furfural at 140°C. The salt-frost treatment increased glucose hydrolysis yields by 147.0 %, achieving 5.68 g/L within 12 hours compared to untreated samples. It emphasizes the significant relationship between porous structure and treatment intensity. This study introduces an energy-efficient approach suitable for high-altitude regions, providing practical insights into the processing of woody biomass. • Salt-frost treatment disrupts the dense structure of poplar. • Salt-frost pretreatment reduced water saturation from 10.1 % to 5.2 %. • Salt-frost pretreatment reduces the hydrothermal process intensity by 84.0 %. • Sodium chloride salt-frost enhances enzymatic hydrolysis by 147.0%, yielding 5.68 g/L in 12 h compared to untreated group.