Pretreatment of agricultural lignocellulosic biomass for fermentable sugar: opportunities, challenges, and future trends

The biofuel yield from lignocellulose biomass depends strongly on the fermentable sugar yield from the hydrolysis step. Enzymatic hydrolysis, the preferable hydrolysis method, gives low sugar yield due to the lignin existence and the cellulose crystallinity. To increase the sugar yield, pretreatment is required to breakdown the recalcitrant nature of lignocellulose biomass. This review paper presents a comprehensive critical review of the lignocellulosic biomass (LCB) pretreatment methods for enhanced fermentable sugar yield. There is a need for an effective and cost-efficient pretreatment method that curbs inhibitory products and reduces the use of chemicals and energy. This paper highlighted recent advances in agricultural-based LCB pretreatment; discussed current challenges, advantages, and disadvantages; and suggested future solutions for agricultural-based biofuel production. Examined methods include pulsed electric energy (PEE), ionic liquid, co-solvent enhanced lignocellulosic fractionation pretreatment, and deep eutectic solvent. Each method was reviewed by its conditions (indicate the use of energy and chemicals), sugar yield, and inhibitory products. The review also researched the synergistic effect of combining more than one pretreatment method as a potential approach to overcome the drawbacks of the individual methods. In addition, the paper suggested improvement for each method and identified the research gaps to be bridged. Also, a comparison, summary, and research perspectives were provided.