Process Optimization of Bioethanol Production from Peels of Yam and Cassava as well as Yam–Cassava Peels Blends

Abstract

The valorization of agricultural residues into bioethanol offers a sustainable route toward low-carbon energy systems. This study examines yam (Dioscorea rotundata) and cassava (Manihot esculenta TME 419) peels as two possible feedstocks for second-generation bioethanol production. Acid–enzymatic hydrolysis and yeast fermentation were optimized using a Box–Behnken design and analyzed with Support Vector Regression (SVR). The most important factors controlling yield were fermentation time, pH and substrate loading, with specific trade-off behaviors depending on substrate. Yam peels exhibited a substrate–time trade-off: prolonged fermentation (118.8 h) at low substrate loading (24.44% v/v, pH 5.13) produced 8.95 % v/v ethanol (±6 %), while SVR predicted 8.39 % v/v achievable in only 6 h at higher substrate loading (79.61% v/v, pH 6.51). Cassava peels displayed a pH–time trade-off, achieving an RSM desirability optimum of 9.5 % v/v at pH 5.52 in about 13 h and an SVR-predicted maximum of 10.31 % v/v at 120 h. Yam–cassava blends yielded 0.52–3.50 % v/v, with the 3:1 cassava–yam ratio performing best. The RSM–SVR framework (R² > 0.95, RMSE < 0.6 % v/v) captured nonlinear fermentation dynamics, revealing fast–high and slow–low regimes. These results confirm yam and cassava peels as low-cost, sustainable feedstocks for decentralized bioethanol production and circular bioeconomy advancement.