Ultrasonication‐assisted acid pretreatment enhances ethanol yield from water hyacinth: comparison with ozonation and life cycle assessment studies

Abstract Ligno‐cellulosic biomass such as water hyacinth represents a sustainable and underutilized feedstock for second‐generation bioethanol production. However, its recalcitrant structure requires effective pretreatment to improve enzymatic hydrolysis and fermentation efficiency. In this study, non‐thermal pretreatment strategies, namely ultrasonication and ozonation, were investigated in combination with dilute sulfuric acid treatment. The performance of these hybrid processes was evaluated through compositional analysis, structural characterization, ethanol yield, and life cycle assessment. Among the tested approaches, ultrasonication combined with acid pretreatment demonstrated the highest ethanol production (71.7 ± 0.28 mg mL −1 ), representing a 41% increase compared with acid treatment alone (50.8 ± 0.42 mg mL −1 ). In contrast, ozonation combined with acid treatment resulted in a lower yield (42.1 ± 0.21 mg mL −1 ). Scanning electron microscopy revealed that ultrasonication induced pore formation on the biomass surface, enhancing cellulose accessibility, whereas ozone treatment caused surface disruption without corresponding improvements in glucose recovery. Fourier transform infrared analysis indicated a reduction in lignin and hemicellulose‐associated bands across treatments, while X‐ray diffraction showed the highest crystallinity index (CrI) for acid pretreatment (81.6%), followed by ozonation (80.4%) and ultrasonication (74.1%). Interestingly, despite its lower CrI and lignin removal, ultrasonication achieved superior ethanol yields, highlighting the importance of microstructural modification and improved enzyme–substrate interactions. The life cycle assessment further emphasized the sustainability advantage of ultrasonication, which exhibited the lowest environmental burdens per kilogram of ethanol. By contrast, ozonation displayed the highest environmental emissions. Overall, ultrasonication emerges as an eco‐effective and scalable pretreatment pathway for valorizing aquatic weeds into renewable bioethanol.