Grey relational analysis-based optimisation of bioethanol production process parameters derived from cassava peels

The emissions from fossil fuels causes severe air pollution and greenhouse gas emissions, driving climate change and health risks. Thus, finding renewable and eco-friendly alternative fuels is urgently needed for energy security and environmental sustainability. This study aimed to produce bioethanol from cassava peels and optimize the production parameters to maximize bioethanol yield and purity. The experimental design was developed using Taguchi orthogonal array, while Grey Relational Analysis and Analysis of Variance were applied to determine the optimal process conditions and evaluate the significance of process parameters. The produced bioethanol was characterized using Fourier Transform Infrared Spectroscopy (FTIR) analysis and physicochemical properties determination. Cassava peels were collected, washed, sun-dried, and ground into powder before undergoing acid hydrolysis using 0.5 M H₂SO₄ at 121 °C to produce fermentable sugars. The hydrolysate was neutralized and fermented with Saccharomyces cerevisiae at controlled temperatures and fermentation times, followed by distillation to obtain bioethanol. The results indicated that optimal conditions of 30 °C fermentation temperature, pH of 4, and 72-h fermentation time produced the highest grey relational grade, corresponding to 33% yield and 96% purity. Furthermore, FTIR spectroscopy confirmed the presence of functional groups and compounds characteristic of ethanol-based biofuels. The produced bioethanol shows physicochemical properties that closely match those of pure ethanol and comply with fuel-grade ethanol standards. These findings demonstrate that cassava peels can serve as an effective feedstock for sustainable bioethanol production, and that optimisation of fermentation parameters significantly enhances fuel quality and production efficiency.