Enhancement of Enzymatic Hydrolysis and Ethanol Production from Pine Chips by Steam Explosion–KOH Treatment with Agricultural Reuse of Liquid Residues

Abstract

Lignocellulosic biomass is a widely available renewable resource, yet its recalcitrant structure limits enzymatic hydrolysis and bioethanol production. This study aimed to develop an efficient pretreatment method for pine wood chips by integrating steam explosion with potassium hydroxide (KOH) treatment and to explore the reuse potential of the resulting liquid waste. Steam explosion disrupted chip structure and exposed cellulose, while subsequent KOH pretreatment selectively removed lignin and hemicellulose, thereby enhancing enzymatic accessibility. Response surface methodology identified optimal conditions of 2.9 min steam explosion, 1.4% KOH, and 21 h treatment time, which yielded a maximum glucose conversion of 30% (based on raw material). The combined process increased ethanol production, with yields approximately sevenfold higher than untreated controls. In addition, liquid waste containing potassium elements promoted the growth of red lettuce, perilla, and green onion, with perilla showing a fivefold increase in fresh weight compared to controls. These findings demonstrate that steam explosion coupled with KOH pretreatment not only improves the efficiency of bioethanol production but also offers a sustainable route for recycling liquid residues as agricultural fertilizer.