Lignocellulosic valorization of groundnut shells for bioethanol: Energy potential and techno-economic feasibility

Abstract

This study investigates optimized calcium oxide (CaO) alkaline pretreatment to create sustainable bioethanol production from groundnut shell waste while evaluating its physical and chemical properties alongside bioenergy capabilities. The versatile properties of groundnut shells obtained from agricultural residues include low moisture content (9.5% wet basis), together with high volatile matter (70.2%) as well as fixed carbon (18.1%), while maintaining low ash content (3.2%) which makes these shells suitable for thermal and biochemical conversions. Their lignocellulosic composition is 32.8% cellulose, 20.1% hemicellulose, and 27.4% lignin. CaO pretreatment at 2% w/v concentration led to improved biomass digestibility, which produced total sugars at 465.2 mg/g and reducing sugars at 297.4 mg/g from the material. Enzymatic hydrolysis of the pretreated biomass achieved an additional glucose concentration of 318.7 mg/g. When Saccharomyces cerevisiae fermented the hydrolysate for 120 hours, it produced 33.6 g/L of ethanol, representing 88% theoretical yield. The pretreatment and subsequent hydrolysis stages yielded reducing sugar recovery rates of 86.5% and 84.1%, respectively, and total sugar recovery rates of 91.6% and 88.3%. Groundnut shells provide a substantial promise as a renewable energy resource because they have a 17.2 MJ/kg heating value and 13.9 MJ energy potential per kilogram of dry biomass. The integrated approach demonstrates the technical viability of bioethanol production from groundnut shells while contributing to sustainable agricultural practices and waste management, and operating within low-carbon energy systems of the circular bioeconomy framework.