Bioethanol Production from Dilute Acid-Pretreated Rice and Sorghum Biomass via Enzymatic Hydrolysis and Fermentation
No Thumbnail Available
Date
2025-09
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Kenyatta University
Abstract
The world has a massive energy need, and bioethanol is a viable clean energy substitute for the
fast-depleting fossil fuel supply. Large volumes of crop leftovers generated and left in the field
for burning can be used in an affordable, dependable, and steady way thanks to production of
bioethanol from lignocellulose biomass. However, because of the variations in lignocellulosic
biomass, biochemical composition and lignin’s recalcitrance, producing ethanol from it is still
difficult. This study evaluated the effects of pre-treating selected agro wastes with dilute acid
on ethanol yields via microbial hydrolysis and fermentation. Nerica husk (NH), Nerica straw
(NS), Basmati 370 husk (BH), Basmati 370 straw (BS), sorghum from KALRO plot 8 (SP08)
and Sorghum from KALRO plot 17 (SP17) were used in this study. Biomass samples were
dried to a constant moisture content, milled into fine powder, and treated at 121oC for 60 min
with sulphuric acid (1.2%(w/w) or 2.25%(w/w) at a solid to liquid ratio of 1:10. This was
followed by enzyme hydrolysis using cellulase from Aspergillus niger at 5% substrate loading.
High performance liquid chromatography (HPLC) with a reverse phase column and refractive
index detector was used to evaluate the resultant sugars. The cellulase hydrolysed substrate
solution was fermented with Saccharomyces cerevisiae, and the alcohol production was
measured by HPLC. An analysis of the statistics was done through the analysis of variance
(ANOVA), considering a 95% confidence level using SPSS software. Simple sugars including
glucose, sucrose, maltose, and specific sugars such as xylose, arabinose, and mannose were
detected, with glucose being the sugar that was found to be most prevalent in all samples.
Glucose yields were consistently higher in samples pre-treated with 2.25%(w/w) dilute
sulphuric acid than in biomass samples pre-treated with 1.2%(w/w) sulphuric acid, which
yielded between 12.8%(w/v) and 26.7%(w/v) glucose across all biomass samples. In contrast,
cellulase hydrolysis after 2.25%(w/w) acid pre-treatment, yielded 32.3%(w/w), 30.6%(w/w),
31.6%(w/w), 30.3%(w/w), 29.3%(w/w), and 13.4%(w/w) glucose from NH, NS, BH, BS,
SP08, and SP17 samples, respectively. Biomass samples pre-treated with 2.25%w/w dilute acid
and subjected to microbial fermentation produced ethanol ranging from 5.8%(v/v) to
8.9%(v/v). These findings demonstrate that 2.25%(w/w) sulphuric acid pre-treatment
significantly enhances the release of fermentable sugars, particularly glucose from selected
agro-wastes, supporting their potential as viable low-cost feedstocks for sustainable bioethanol
production in Kenya
Description
A Research Thesis Submitted in Partial Fulfilment of the Requirements of the Award for the Degree of Master of Science in Biotechnology in the School of Pure and Applied Sciences, Kenyatta University, September 2025
supervisor:
1.Eliud NM Njagi
2.George I Omwenga