Optimisation of Bioethanol Production from Sweet Sorghum Juice Using Response Surface Methodology and Techno-Economic Analysis for North Central Nigeria

Sweet sorghum is a drought-tolerant energy crop with an established cultivation base in the North Central geopolitical zone of Nigeria, offering high juice sugar content suitable for direct fermentation to bioethanol without energy-intensive pretreatment required for lignocellulosic feedstocks. This study optimises the fermentation conditions for bioethanol production from sweet sorghum juice harvested from cultivar Kari Sorghum-1 grown in Nasarawa State and conducts a techno-economic analysis for a 5,000-litre per day production scale. Process variables optimised by response surface methodology using a Box-Behnken design included inoculum concentration, temperature, initial sugar concentration, and fermentation time. Ethanol yield and productivity were the response variables. Statistical analysis confirmed significant quadratic and interaction effects for all four variables on ethanol yield. The optimum conditions of 10.8% inoculum, 32 degrees Celsius, 200 g/L sugar, and 68 hours produced an ethanol yield of 0.47 g/g sugar (92.2% of theoretical), with productivity of 1.38 g/L/h. A process flow simulation in SuperPro Designer was used to develop mass and energy balances and size major equipment for the proposed facility. Capital expenditure was estimated at 186 million Naira, with a minimum ethanol selling price of 482 Naira per litre at a 20-year project lifetime and 10% discount rate. The study establishes the economic feasibility boundary conditions for sweet sorghum bioethanol in North Central Nigeria. Keywords: sweet sorghum, bioethanol, response surface methodology, techno-economic analysis, Nasarawa State