Production of Bioethanol from Watermelon Peel Using Dilute Acid Hydrolysis and Fermentation
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Date
2019-06
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Addis Ababa University
Abstract
The objective of this study was the production of bioethanol from watermelon peel in order to
minimize the energy cost and substitute the non-renewable energy by using renewable resources.
The conversion of watermelon peel to ethanol can be achieved mainly by four process steps.
Pretreatment of watermelon peel to remove different contaminants, drying at 65°C for 48 h,
followed by grinding to the particle size of 2 mm are the initial steps. Then, after soaking in
dilute acid, the pretreated watermelon peel was converted into reducing sugar (glucose). This
followed by the fermentation of the sugars to ethanol using Saccharomycese cerevisiae and
distillation. Box Behnken Design (BBD) designed the experiment with three factors (mass of
reducing sugar concentration, pH and Inoculum level). Seventeen runs were carried out and
analyzed using Design Expert 11 software, to investigate the effects of fermentation parameters
on yield of ethanol. The mass of reducing sugar was varied from 2.551g to 4.891 g, pH was
varied from 4 to 6 and Inoculum was varied from 10 to 20 mL during fermentation. The
maximum yield was observed at inoculum level of 15 mL; mass reducing sugar 3.721g and a pH
of 5. Mass of reducing sugar and inoculum level has a statistically significant effect on the yield
with p-values of 0.0082 and 0.0001, respectively. However, high inoculum level causes a decline
in the ethanol yield. The statistical analysis also showed that the ethanol yield of (0.482mL/g)
were obtained at optimized values of the variables, 3.698 g mass of reducing sugar, 5.02 pH, and
inoculum level of 15.82 mL. This reveals a good agreement with the observed value of the
ethanol yield (0.497 mL/g). Characterization of the bioethanol produced was performed using
Fourier Transform Infrared Spectroscopy (FTIR) and High Performance Liquid Chromatography
(HPLC). From result, it was observed that the ethanol produced from watermelon peel contains
OH, CO, CH2, and CH3 functional groups, when compound with standard ethanol confirming the
presence of ethanol in the product. The HPLC result showed that the product (Bioethanol) had an
RT value of 21.871 min similar to the RT value of 21.86 min for the standard, confirming the
presence of ethanol.
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Keywords
Bioethanol, watermelon peel, hydrolysis, fermentation and Saccharomycese cerevisia, FTIR, HPLC