Bioethanol Production Via Fermentation of Waste Substrates Using Yeast Isolates

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Addis Ababa University


Bioethanol is one biomass derived platform molecules which has a potential to be a sustainable feedstock for a variety of commodity chemicals. The aim of this study was to produce bioethanol from grain waste flour, tella spent, pineapple and papaya peels. Dilute sulfuric acid was used to hydrolyze polysaccharide in the raw materials. Starch content in grain waste flour and reducing sugar concentration in the hydrolysates of each raw material was determined. Indigenous yeast was isolated from areki difdif and tej samples. Indigenous yeast isolates with high fermentation efficiency and high ethanol producing ability were used to ferment hydrolysates in each of raw material to bioethanol. The results indicate that pretreatment of grain waste flour, papaya peels, pineapple peels and tella spent with 2% sulfuric acid at 110oC for 90 minutes yielded 29.7–30.8, 28.2–28.9, 16.2–16.6 and 10.3–10.5% of reducing sugar, respectively. The yeast isolate 1T-10 from tej samples was efficient in converting the D-glucose to ethanol (75.58%) and produced highest yield of ethanol (7.72%) from 20% D-glucose compared to other yeast isolates. Fermentations of grain waste flour with 1T-10 produced the highest yield of ethanol 1.380% (w/v) from pretreatment of substrates with 2% sulfuric acid at 168 hours of fermentation time compared to other combinations or 0% at (72, 120 and 168 hours), 1% at (72, 120 and 168 hours), 1.5% at (72, 120 and 168 hours) and 2% at (72 and 120 hours). Similarly, fermentation of pineapple peels, papaya peels and tella spent produced the highest yield of ethanol; 7.883%, 6.400% and 4.813% (w/v) with pretreatment of 2% sulfuric acid at 120, 72 and 72 hours of fermentation time, respectively compared to other combinations when fermented with the same yeast isolate (1T-10). It was concluded from the present study that it is possible to produce economically viable bioethanol by digesting waste and cheap resources like grain waste flour, tella spent, pineapple and papaya peels using indigenous yeast isolates.



Bioethanol, Tella Spent, Grain Waste Flour, Tej, Areki Difdif, Indigenous Yeast