Evaluation of Bioethanol Quality Produced by Sweet Sorghum Stalks in Uganda

Sweet sorghum (Sorghum bicolor) is a drought-tolerant plant with high sugar content and low input requirements, making it a promising candidate for bioethanol production. This study aimed to assess bioethanol production from local sweet sorghum varieties in Uganda. Six varieties with brix content ranging from 10% to 25% were screened, and juice was extracted and fermented using the SC yeast strain for 10 days, followed by fractional distillation to produce bioethanol. The feedstock was characterized by protein, reducing sugars, and carbohydrate content. Using response surface methodology (RSM) and a central composite design, 20 experimental runs were conducted to optimize yeast loading, reaction time, and agitation rate. The optimal parameters identified were 25 g of yeast loading, 10 days of reaction time, and an agitation rate of 100 rpm. The resulting bioethanol concentrations from the sweet sorghum juice ranged from 56 % v/v to 90% v/v, while concentrations from the bagasse ranged from 15% v/v to 40% v/v. The higher heating value (HHV) of the bioethanol produced varied from 12.46 MJ/kg to 16.79 MJ/kg. Quality assessments using bomb calorimetry, density pycnometry, and fire and flash point tests revealed HHVs between 13.06 MJ/kg and 20.31 MJ/kg, juice densities of 0.82 g/cm3 to 0.87 g/cm3, bagasse densities of 0.90 g/cm3 to 0.96 g/cm3, and flash points ranging from 17.8°C to 23.0°C for juice and 25.5°C to 45.3°C for bagasse. This study demonstrates that local sweet sorghum stalks have significant potential for bioethanol production, offering a sustainable alternative to fossil fuels in developing countries.