Hydrothermal pretreatment optimization for enhanced anaerobic digestion of willow sawdust

Lignocellulosic biomass including agricultural and forestry residues such as willow sawdust could be used as feedstock for anaerobic digestion (AD). Hydrolysis has been shown to be the rate-limiting step in the case of AD of such substrates. Although being abundant, since the annual world production of biomass residues exceed 220 billion tons, the main obstacles of their use are the low yields attained, due to the recalcitrant nature of their lignocellulosic content. The application of a pretreatment process prior to AD could improve the hydrolysis and the total methane yield. In this study, hydrothermal pretreatment alone or in combination with HCl, at a chemical loading of 2 g /100 g TS was carried out as a pretreatment method to enhance anaerobic digestion of willow sawdust, through biochemical methane potential (BMP) experiments. For both pretreatment approaches, various temperatures (130.5-229.5 oC) and process times (15.6 -59.4 min) were studied. Following pretreatment, the insoluble solids and the hydrolysates were separated by filtration and fully characterized in terms of their structural and chemical characteristics. BMP experiments showed that the hydrothermal pretreatment alone or in combination with the acid enhanced the methane yields and the higher the temperature or process time, the higher the yields which were obtained.