A critical review of sustainable biorefineries utilizing high-solid processing for industrial crop lignocellulosic wastes valorization

Biorefinery has been recently one of the most popular topics studied by researchers to utilize industrial crop lignocellulosic wastes for producing energy carriers and chemical compounds. High-solid processing (>15% w/w) offers benefits, including improved sustainability, increased productivity, low operational costs, and reduced environmental impact compared to low and moderate content processing. Despite this, lignocellulosic biorefineries have not significantly contributed to large-scale fuel and chemical production because of technological challenges and economic feasibility. There are difficulties in process control, sufficient mixing, separation, and purification of desired products, continuous operation, and scale-up associated with using high solid loading processes. Furthermore, the processing of high-solid content materials in biorefineries demands custom-made reactor designs and equipment that can efficiently handle the solids and enhance productivity. This issue poses a challenge in the development of biorefineries. This review aims to comprehensively analyze the status of high-solid processing in various areas of refining industrial crop wastes, including pretreatment, enzymatic hydrolysis, fermentation, and separation. Several industrial applications of high-solid processing in biorefinery development, such as biofuels and value-added products, are also discussed in detail.