Bioethanol production from biodegradable wastes using native yeast isolates from Ethiopian traditional alcoholic beverages

Abstract

Due to the existing energy crisis and scarcity of conventional supplies of fossil fuels, there is a strong desire for the production of bioethanol from sustainable biodegradable waste as an alternative energy source. The aim of this study was to produce bioethanol from grain waste flour (GWF), Tella spent (TS), pineapple (PAP) and papaya peels (PYP) using native yeasts isolated from Ethiopian traditional alcoholic beverages. Diluted H2SO4 was used to hydrolyze polysaccharides in the waste materials. Starch content from GWF and reducing sugar concentration from each hydrolysate were determined by the standard protocol. Seventy-five native yeasts were isolated from local beverages for ethanol production. The 2% H2SO4 pretreatment produced the highest reducing sugar of GWF (30.1%); PYP (28.6%); PAP (16.4%); and TS (10.4%). In addition to this, GWF had 60.6% starch content. Of 75 isolates, 12 were able to tolerate ≥8% ethanol concentration, and 2 isolates, Y10 and Y55 showed strong ethanol production capacity (glucose to ethanol conversion efficiency) with 8.2% (79.8%) and 9.6% (94.3%) from synthetic medium, respectively. The highest ethanol yields of 16.1%, 9.8%, 8.0% and 6.1% were produced from GWF, PAP, PYP and TS, respectively using isolate, Y55 (identified as S. cerevisiae) within 168 h for GWF, 120 h for PAP and 72 h for PYP and TS. This study revealed that native yeast isolates could be used for industrial production of bioethanol via cheap biodegradable wastes.