Abstract
The accelerating global demand for renewable energy has intensified interest in bioethanol as a sustainable and economically viable alternative to fossil fuels. In this study, ethanol production from sugar beet molasses—an abundant, nutrient-rich agro-industrial residue—was systematically optimized using Zymomonas mobilis PTCC 1718. A Central Composite Design (CCD) under Response Surface Methodology (RSM) was employed to quantify and model the interactive effects of five critical fermentation variables: temperature, pH, sucrose concentration, agitation rate, and fermentation time. The statistical model exhibited excellent predictive capability (R² = 0.991), enabling precise determination of optimal operating conditions. Using molasses equivalent to 150 g/ L sugar, a maximum ethanol concentration of 41.41 g/ L was achieved at 30 °C, pH 6.0, 15 % sucrose, 100 rpm, and 72 h, corresponding to a yield of 0.276 g ethanol / g sugar (54 % of theoretical) and a productivity of 0.575 g/L /h. The response trends and factor interactions were in strong agreement with the physiological behavior of the microorganism, confirming the robustness of the model. Comparative evaluation with previous studies further demonstrated the superior fermentative performance of Z. mobilis and validated sugar beet molasses as a cost-effective and sustainable feedstock. Overall, the findings provide a scalable process framework for high-yield bioethanol production while contributing to waste valorization and advancing circular bioeconomy strategies.