Effects of redox environment on hydrothermal pretreatment of lignocellulosic biomass under acidic conditions

The effects of the redox environment on acidic hydrothermal pretreatment were investigated in experiments with sugarcane bagasse (190 degrees C, 14 min) and Norway spruce (205 degrees C, 5 min). To modulate the redox environment, pretreatment was performed without gas addition, with N-2 , or with O-2. Analyses covered pretreated solids, pretreatment liquids, condensates, enzymatic digestibility, and inhibitory effects of pretreatment liquids on yeast. Addition of gas, especially O-2 , resulted in increased severity, as reflected by up to 18 percent units lower recoveries of pretreated solids, up to 31 percent units lower glucan recoveries, improved hemicellulose removal, formation of pseudo-lignin, improved overall glucan conversion, and increased concentrations of several microbial inhibitors. Some inhibitors, such as formaldehyde and coniferyl aldehyde, did not, however, follow that pattern. TAC (Total Aromatic Content) values reflected inhibitory effects of pretreatment liquids. This study demonstrates how gas addition can be used to modulate the severity of acidic hydrothermal pretreatment.

Automated summary

The study demonstrates that the redox environment during acidic hydrothermal pretreatment can impact the separation efficiency and formation of inhibitory substances. Specifically, the addition of oxygen increases the severity of the treatment, leading to lower recoveries of solids and glucan, as well as the production of new microbial inhibitors.