Enhancing biofuel yield from biomass of the invasive plants Ludwigia hexapetala and Ricinus communis through silver nanoparticles integration

Abstract

This study explores the bioethanol production potential of two invasive plant species, Ludwigia hexapetala (LH) and Ricinus communis (RC), using an innovative approach that incorporates silver nanoparticles (AgNPs) during biomass processing. AgNPs were synthesized and integrated into the biomass to enhance enzymatic hydrolysis and fermentation, as evident from the Transmission Electron Microscopy (TEM) analysis. Detailed chemical analyses revealed significant improvements in the treated biomass. Cellulose content increased from 35.2 to 40.8% in LH and 32.5 to 37.9% in RC after AgNP treatment. Concurrently, lignin contents decreased from 18.4% to 15.6% in LH and from 20.1% to 17.4% in RC, facilitating better enzymatic access. Fibre composition analysis confirmed reductions in neutral digestible fibre (NDF) from 53.2 to 49.7% in LH and 54.1 to 51.5% in RC, along with an overall improvement in biomass porosity. These structural changes enhanced enzymatic hydrolysis efficiency, with reducing sugar yields increasing from 92.8 to 118.3 mg/g in LH and 84.5 mg/g to 109.1 mg/g in RC at an optimal enzyme loading of 20 FPU/g. AgNPs treatment also reduced the phenolic content, which inhibited microbial activity, from 71.4 to 65.2 mg EGA/g in LH and 76.8 to 70.3 mg EGA/g in RC, ensuring smoother fermentation. Fermentation experiments showed that ethanol yields were significantly higher in AgNP-treated biomass, with LH-AgNPs achieving 71.4 g/L ethanol (93.4% of theoretical yield) and RC-AgNPs producing 69.2 g/L ethanol (91.7% of theoretical yield) after 72 hours. In contrast, untreated LH and RC produced 61.8 g/L (82.4%) and 60.1 g/L (80.5%) ethanol, respectively. Glucose consumption was more efficient in treated samples, with residual glucose levels reduced to 7.1 mg/L for LH-AgNPs and 8.4 mg/L for RC-AgNPs, compared to 12.5 mg/L and 15.2 mg/L in the raw counterparts.