Valorization of Sorghum Stalk Residues for Bioethanol Production: A Sustainable Pathway to Agricultural Waste-to-Energy Conversion

The renewable biomass waste from sorghum stalks, which farmers burn in open fields, results in environmental harm. Flexible approaches for waste energy conversion generate efficient second-generation bioethanol from sorghum stalks. This study explores the sustainable bioethanol production from sorghum stalk waste through optimized CaO alkali pretreatment. Scientists studied sorghum stalks, which constitute agricultural waste, as a raw material for lignocellulosic content determination to identify their high levels of cellulose (38.3%) and hemicellulose (27.4%). A pretreatment using 2% w/v CaO solution resulted in the greatest total sugar production of 465.2 mg/g, together with maximum reducing sugar level at 297.4 mg/g. The glucose yield from pretreated biomass increased to 318.7 mg/g after enzymatic hydrolysis was performed. After 72 hours of Saccharomyces cerevisiae fermentation of the hydrolysate, an ethanol concentration of 19.6 g/L was attained, reaching a theoretical yield of 78.4%. The total reducing sugar recovery rate throughout pretreatment came to 91.6%, and the reducing sugar recovery rate marked 86.5%, but during hydrolysis, the recovery reached 88.3% (total sugar) and 84.1% (reducing sugar). Scientists have determined the renewable energy potential of sorghum bioethanol by establishing that it provides 13.9 MJ of energy for every kilogram of dry biomass. Therefore, this studyindicates that the proposed process delivers both economical benefits and environmental advantages according to assessed technical-economic calculations. Also, the study establishes that transforming sorghum stalk waste into bioethanol is possible through this process, which benefits sustainable agricultural systems and the circular bioeconomy framework and contributes to worldwide renewable energy system development with low-carbon emissions goals.