Abstract:
Lignocellulosic biomass is one of the most suitable alternative energy sources, whichcan be
harnessed to meet the challenges of energy security. Energy resources such as petroleum and
coal are being utilized at a rapid rate and eventually run out. Therefore, this research was
initiated to find an alternative substrate for the production of ethanol from a cost-effective
substrate. Parthenium leaf and stem were collected from Haramaya University. The collected
Parthenium leaf and stem washed and dried in an oven and ground to powder form by a
grinding machine. The powders of Parthenium leaf and stem with different concentrations
(50gm, 60gm, 70gm, and 80gm) were treated with sodium hydroxide (alkali pre-treatment). The
inocula(1% and 2% Saccharomyces cerevisiae) with 100ml nutrient solution were added to each
substrate concentration separately and the pH of the solution was adjusted to 4.5 and allowed to
ferment for 15days at 30OC to determine cell denity, reucing sugar and for ethanol production.
In this study, the highest cell density was observed on the 9th day of the fermentation period with
60grams of substrate inoculated at 2% inoculum concentration. The cell density decreased
gradually as the fermentation period increased. Maximum bio-ethanol production of pre-treated
Parthenium leaf and stem (22.50%) was achieved on the 9th day of fermentation from 60gm of
substrate inoculated with 2% yeast suspension. Moreover, on the 3rd day of the fermentation
period, the highest reducing sugar concentration (27.75mg/ml) was obtained from 60gm of alkali
pre-treated substrate inoculated with 2% Saccharomyces cerevisiae, whereas the same substrate
concentration showed 20.22mg/ml in the untreated substrate. Within time of fermentation, the
bio-ethanol yield and cell density also increased up to the 9th day of the fermentation. In this
study, the effect of alkali pre-treatment on bio-ethanol production was also examined. The result
showed that a 60-gram substrate with 2% Saccharomyces cerevisiae showed as optimum for
ethanol production and the alkali pre-treated samples yielded more ethanol than the untreated
samples.
