Utilization of Agrowastes for Bioethanol Production using Separate Hydrolysis and Fermentation

Abstract

This study investigates the potential of water yam and white yam peels as sustainable substrates for bioethanol production. Aspergillus niger and Saccharomyces cerevisiae were isolated and identified using microbiological and molecular methods.  Aspergillus niger was used to carry out enzymatic hydrolysis on the substrates and Saccharomyces cerevisiae was subsequently used for fermentation. The physical properties of the bioethanol distillates, including boiling point, density, and specific gravity, were evaluated. Proximate analysis and nutrient content across the substrates were determined. Fermentation was carried out at varying temperatures and pH levels to determine the optimal yield parameters. Gas Chromatography-Mass Spectrometry (GC-MS) and Fourier Transform Infrared Spectroscopy (FTIR) were employed to assess the quality and structural properties of the bioethanol produced. The results showed that water yam peels had higher moisture, fibre, and protein content than white yam peels (P < 0.05). The yield from white yams was 4.93% (v/v) compared to 4.43% (v/v) from water yams. The highest reducing sugar and ethanol yields were obtained from white yam peels, yielding a reducing sugar concentration of 1.86 g/L and an ethanol yield of 4.73 ± 0.21% (v/v). In contrast, water yam peels yielded 1.66 g/L of reducing sugar and 4.23 ± 0.31% (v/v) ethanol. These results demonstrate the feasibility of utilizing water yam and white yam peels as locally sourced raw materials for bioethanol production, contributing to biofuel development in regions with abundant yam resources.