Bioethanol production from melon peel waste by simultaneous saccharification and fermentation using Zymomonas mobilis : process optimization by response surface methodology

Fruit-processing wastes have attracted increasing attention as renewable feedstocks for second-generation bioethanol production due to their high carbohydrate content and low economic value. In this study, melon peel waste (Cucumis melo L.) was evaluated as a substrate for bioethanol production through simultaneous saccharification and fermentation (SSF) using Zymomonas mobilis. A Box–Behnken design coupled with response surface methodology (RSM) was applied to assess the effects of temperature (30–50 °C), pH (4.0–7.0), enzyme loading (10–40 U/g substrate), and fermentation time (24–72 h) on ethanol production and to identify optimal conditions. The quadratic model was highly significant (p < .0001) and showed good agreement with experimental data (R2 = 0.9727). Ethanol concentrations ranged from 4.3 to 18.0 g/L. Fermentation time and enzyme loading were the most influential factors affecting ethanol production. The model predicted maximum ethanol production at 35.6 °C, pH 5.7, an enzyme loading of 38.7 U/g substrate, and a fermentation time of 71.2 h. Validation experiments produced 18.5 g/L ethanol with a yield of 0.483 g ethanol/g consumed sugar. This study demonstrates the potential of Iranian melon peel waste as a feedstock for bioethanol production and confirms the usefulness of RSM for optimizing the SSF process.