Valorizing agricultural residues as biorefinery feedstocks: current advancements and challenges

Abstract Biological pretreatment using microorganisms has been identified as a promising approach to degrade lignocellulosic structure extracellularly, thus increasing the sugar conversion rate of the agricultural biomass. They have several attractive traits such as eco-friendly and simple operation, low capital cost, low energy requirement, and no chemical requirement. Major drawbacks are long pretreatment time and strict microbial growth conditions. The direct use of ligninolytic enzymes extracted from microorganisms on lignocellulosic biomass emerges as an alternative approach to eliminate the abovementioned problems. Besides, the application of advanced biotechnologies to extract enzymes is expected to genetically enhance the lignin-degrading properties suitable for industrial practice. Advanced biotechnologies could help to reduce the current bottleneck (cost of enzyme extraction and purification) of biological pretreatments. The capability to recover and reuse enzymes from the pretreatment process can reduce the overall expenditure. Effective separation and recovery of energy products (e.g., ethanol and methane) from the conversion process will also contribute to increasing the cost effectiveness. This chapter aims to present a succinct overview of the status of technologies for agricultural residues to produce and recover bioenergy and biochemicals from the conversion of their lignocellulosic components. It is envisioned that further technical improvements will allow agricultural residue biorefinery to become a domain sector in the sustainable harvesting of green energy and biochemicals.