Co-production of biogas and hydrochar from the mixture of sawdust and brewer's spent grain

Abstract

<b><sc>Abstract.</sc></b> Lignocellulosic biomass are plentiful low-cost resources available in nature having significant bioenergy potential with a low environmental burden. Sawdust, one of the major low-value byproducts of wood processing facilities, is such an abundant feedstock. Brewer‘s spent grains (BSG), a major byproduct of the brewing industry, is another high potential feedstock for bioenergy production. The objective of this work is the co-production of biogas and hydrochar using integrated anaerobic digestion (AD) and hydrothermal carbonization (HTC) processes from a mixture of sawdust (from sugar maple) and brewer‘s spent grains (BSG). A two-step mechanical hydrothermal pretreatment, combining liquid hot water pretreatment followed by disk milling, was used to reduce the biomass recalcitrance. Various mixtures of raw and pretreated biomass were investigated for biogas production AD for 21 days. The pretreatment was effective in increasing the biogas yield during the AD process. In the case of sawdust, the biogas yield increased by 3.3 folds compared to raw biomass. The co-digestion resulted in high biogas yield, with the maximum biogas yield of 611.1 mL/g VS for a mixture of raw BSG and pretreated sawdust at a 1:4 ratio. The proximate and ultimate analysis of hydrochar obtained from the hydrothermal carbonization of the digestatewere performed to identify the carbon densification and to study the thermogravimetric analysis.