Essential Oil Extraction to Valorize Bioethanol Production from Ginger Stalks and Leaves After Mild Alkaline Infiltration

Lignocellulosic wastes are low-carbon, renewable and sustainable feedstocks for replacing fossil fuels in the production of energy and chemical products. However, the bioconversion of lignocellulose into biofuels or biochemicals is costly. To address the high cost, this study extracted essential oil (EO) from ginger stalks and leaves (GSL) as an antioxidant to valorize the bioconversion process of GSL. The Box–Behnken design was used to optimize EO extraction, and the maximum EO yield of 2.99% was obtained under the optimal condition of KOH infiltration for 26 h, extraction for 3 h, and an n-hexane-to-GSL ratio of 8 (v/w). With 95% n-hexane recovery and no generation of waste liquid during the extraction process, fugitive emissions and solvent waste were reduced, enhancing sustainability. The EO’s antioxidant activity exceeded that of commercial ginger EO. The combined process of KOH infiltration and n-hexane extraction induced physicochemical changes in GSL and improved its enzymatic hydrolysis efficiency from 2.70% to 69.09%. According to the economic assessment, the bioconversion of GSL into bioethanol would benefit from the EO product, with the on-site production cost of cellulase being no more than 0.98 USD/kg. This study presents a feasible and sustainable case for lignocellulosic biorefining.