Impact of hydrothermal pretreatment on anaerobic digestion efficiency for lignocellulosic biomass: Influence of pretreatment temperature on the formation of biomass-degrading byproducts.

Anaerobic digestion (AD) of lignocellulosic biomass is appealing because of the abundance and ease of obtaining the biomass locally. However, the recalcitrance of lignocellulosic biomass presents an obstacle in the hydrolysis step of AD and lowers the process efficiency. In this study, sunflower, which is a model lignocellulosic biomass, was pretreated by thermal (hydrothermal pretreatment, HTP) and non-thermal (milling) methods; the methane yield and biodegradability of the pretreated biomass were determined using a series of batch tests. The thermal pretreatment method showed a significantly higher methane yield (213.87-289.47 mL g VS) and biodegradability (43-63%) than those of the non-thermally pretreated biomass, and the optimum pretreatment effect was observed at an HTP temperature of 180 °C. However, at an HTP temperature exceeding 200 °C, the induced formation of 5-hydroxymethylfurfural and furfural significantly lowered the methane yield and biodegradability. This study revealed that the HTP temperature is closely related to the formation of lignocellulosic biomass-degrading byproducts, which potentially hinder the methanogenesis step in AD; severe HTP conditions may have the opposite effect on the AD performance of lignocellulosic biomass.