A Review of Hydrothermal Pretreatment of Lignocellulosic Biomass for Enhanced Biogas Production

Lignocellulosic biomass is regarded as a promising renewable resource that can be potentially used to provide second-generation biofuels or to produce chemicals. Hydrothermal treatment (HTT) of lignocellulosic biomass has received considerable attention because of its feasibility and efficient generation of valuable products. Recently, much attention has been paid to the studies of using HTT as pretreatment of lignocellulosic biomass for biogas production. These studies show that operational parameters (including temperature, retention time, pressure, solid content, particle size and pH) are crucial for lignocellulose conversion into biogas. Up to now, however, no review could be found on this aspect. In order to optimize the pretreatment process for enhanced biogas production, the above-mentioned operational parameters of HTT are summarized and discussed with respect to the pretreatment of lignocellulosic biomass and their enhancement effects on biogasification. Related studies on hydrothermal treatment of lignin, hemicellulose and cellulose are reviewed. The above parameters adopted in the recent research works for biogas production have been critically addressed. In addition, future research directions are also prospected.