Valorization of Deep Eutectic Solvent Pretreated Lignocellulosic Biomass for Improved Biogas Production

Chemical pretreatment is an important method in the valorization of biomass for bioenergy production. The recalcitrant nature of lignocellulosic materials makes them resistant to microbial attacks, which reduces or impairs their usefulness as feedstock for bioenergy production. Although chemical pretreatment has been proven useful and efficient in fractionating lignocellulosic materials/biomass for the production of biofuels and bio-based chemicals, the effects of wastewater generated from the process on the environment have been an issue of great concern. The need for greener solvents to arrest the situation has encouraged significant research efforts in this direction. Chemicals such as ionic liquids (ILs) have been extensively studied, and research is still ongoing. However, some of the undesirable properties of the ILs, which limited their applications, have led to the quest for better solvents, which eventually led to the use of deep eutectic solvents (DESs). Numerous studies have been conducted on the applications of different classes of DESs, including catalysis, extraction, gas adsorption/absorption, purifying and manufacture of biodiesels and metal electrodeposition; however, the use of DESs to pretreat biomass for biogas production via anaerobic digestion (AD) has been sparsely explored. This review seeks to reveal the extent of work done so far in this respect, address the likely challenges, identify untapped possibilities and future research opportunities. Overall, this review provides valuable insights into the use of DESs for lignocellulosic biomass pretreatment and their potential to revolutionize the production of renewable energy from biomass.