Fermentation Engineering of Cassava-Based Bioethanol Production: Process Optimisation, Techno-Economic Modelling, and Scale-Up Analysis for South East Nigeria

Nigeria's escalating fuel import costs and underutilisation of its massive cassava production base create compelling conditions for developing domestic cassava bioethanol as a renewable fuel blend stock and industrial feedstock. South East Nigeria, combining high cassava production density with industrial infrastructure, provides a strategically appropriate context for bioethanol scale-up analysis. This thesis presents a comprehensive fermentation engineering investigation of cassava-based bioethanol production encompassing process optimisation, techno-economic modelling, and industrial scale-up analysis for South East Nigeria. The research programme comprised five integrated components: physicochemical characterisation of cassava starch hydrolysis kinetics using immobilised glucoamylase and alpha-amylase enzymes, optimisation of Saccharomyces cerevisiae fermentation conditions using response surface methodology with a Box-Behnken design across temperature, initial sugar concentration, and inoculum density parameters, development of a validated process simulation model in Aspen Plus for a 50,000-litre per day production facility, comprehensive techno-economic analysis incorporating Nigerian capital cost structures and feedstock pricing dynamics, and environmental life cycle assessment. Response surface methodology optimisation identified optimal conditions of 34 degrees Celsius, initial glucose concentration of 180 g per litre, and inoculum density of 12 g per litre dry cell weight, yielding ethanol titre of 82.4 g per litre and productivity of 2.74 g per litre per hour. Techno-economic analysis projected an internal rate of return of 19.4 percent at 40 Naira per litre cassava feedstock cost with government blending mandate support. Life cycle analysis confirmed 62 percent greenhouse gas reduction versus petroleum petrol. Keywords: bioethanol, cassava, fermentation engineering, techno-economic modelling, South East Nigeria.