Facilitating renewable energy production for a circular bioeconomy: A review of the biorefinery potential, opportunities, and challenges for valorization of sorghum processing residues in sub-Saharan Africa

Sorghum is a multi-purpose crop, with current uses primarily focused on utilizing either the sorghum grain as food or feed, or the stalk for juice and syrup production. However, opportunities exist to fully utilize the entire crop by converting its residues in a biorefinery setup. The reported compositions of the grain and its residues suggest that they are feasible feedstocks for conversion to various products, including bioenergy, biofuels, and specialty chemicals. However, the industrial-scale adoption of sorghum-based biorefineries will depend on their sustainability, which is region-specific. This critical review presents a comprehensive and comparative analysis of the current status and future research needs for converting sorghum residues into bioenergy and other valuable products within the sub-Saharan context. First, production trends and compositions of sorghum and its residues are presented, and potentially recoverable products are identified. Then, technological advances in the conversion of sorghum residues are discussed. Finally, based on the compositions of the residues and characteristics of the recovered products as reported in the literature, potential multi-product biorefineries are suggested. The potential outlook, including challenges to the industrial-scale adoption of sorghum residues-based biorefineries and the potential for improvement within sub-Saharan Africa, is presented. To accelerate adoption at an industrial scale, further research is necessary to identify the most efficient, cost-effective, environmentally friendly, and socially beneficial multi-product sorghum residues-based biorefinery processes for the complete valorization of the crop.