Integrating enzymatic hydrolysis and nanoparticle catalysis for sustainable bioethanol production from pumpkin and dragon fruit pomace by non-conventional yeasts based fermentation prosesses

This study investigated the effects of metal oxide nanoparticles on bioethanol production from lignocellulosic wastes-dragon fruit pomace, and pumpkin pomace-using yeast strains Saccharomyces cerevisiae, Kluyveromyces marxianus, and Candida boidinii. Among the tested substrates, pumpkin pomace yielded the highest ethanol concentrations, particularly at the highest biomass loading (150 g/L). Enzymatic hydrolysis with cellulase was optimized, with 60 FPU/g substrate identified as the most cost-effective loading for maximizing sugar release and ethanol yield. The application of metal oxide nanoparticles (ZnO, Fe₂O₃, and NiO) was explored to enhance fermentation efficiency. NiO nanoparticles at 20 mg/100 mL significantly improved bioethanol production. Without supplementation, 21.93 g/L of bioethanol (Y_{P/S max}: 0.24 g/g, Q_{p max}: 0.18 g/L.h) was obtained from 150 g/L PP. However, when 20 mg/100 mL NiO nanoparticles were added to a 150 g/L pumpkin pomace medium, and the enzyme loading was adjusted to 60 FPU/g substrate, the ethanol concentration increased by 95.8% to 42.64 g/L. Y_{P/S max} and Q_{p max} were found to be 0.40 g/g and 0.89 g/L.h, respectively, in these conditions. These results demonstrate that integrating nanoparticle-assisted hydrolysis and fermentation is an effective, cost-saving approach to enhance bioethanol production from low-value agricultural residues, providing a promising approach for sustainable biofuel generation.