Brook Tesfamichael (PhD)Anteneh Chando2025-10-072025-10-072025https://etd.aau.edu.et/handle/123456789/7472International demand for renewable energy sources has established research into the production of bioethanol at the highest possible levels from agro industrial wastes such as molasses. Maximal production of ethanol from molasses and minimization of waste output to the environment by optimization of yeast growth and molasses fermentation are the prime objectives of this research at Balezaf Alcohol and Liquor Factory (BALF), Ethiopia. Chemical analysis showed 46.02% fermentable sugars and 49.52% reducing sugars in raw molasses. Process conditions, i.e., pH, sugar concentration, temperature, dosage of nutrient, and inoculum of yeast, were optimized by Response Surface Methodology (RSM) and Box-Behnken Design (BBD). The optimum propagation conditions (pH 4.75, 1.0 g/L DAP + urea, and 1.5 g/L yeast) yielded 0.8% ethanol and 3.52 × 10⁸ cells/mL cell count, and optimized fermentation (17% sugar, 30°C, 10% inoculum) yielded 12.1% ethanol with a meager 0.7% residual sugar far better than BALF's customary yields of 6.5–9.5% ethanol and 2–3.5% residual sugar. Recyclable yeast yielded 10.9% ethanol, an enviably rosy reading for cost efficient and eco-friendly production. ANOVA statistical test and model fit (R² > 0.98, p < 0.05) ensured the process reliability. The current study demonstrates the very first complete and scalable optimization method in BALF, an environmentally friendly model of bioethanol production in Ethiopia.en-USFermentation of molassesYeast recyclingYeast propagationResponse Surface MethodologyResidual sugarMinimization of wasteBalezaf Alcohol and Liquor Factory.Thesis