Utilization of sweet potato peels for bioethanol generation by <i>Zymomonas mobilis</i> and <i>Saccharomyces cerevisiae</i> using response methodology

Abstract

Ethanol is one of the bioenergy sources with high efficiency and low environmental impact. In this study, fermentation conditions were optimized based on the central composite design of response surface methodology for maximum ethanol recovery. Under these optimized process conditions, Zymomonas mobilis and Saccharomyces cerevisiae were used to ferment potato peel waste as a sole carbon source. The test variables in a defined range of inoculum concentration (6 % - 14 %), pH (4.0 – 6.0), sugar concentration (14 – 22^oBrix), temperature (24 – 32 ^oC) and the inoculation time (30 – 54hrs) were modeled using the response surface methodology (RSM). The experimental data indicated that the maximum ethanol production observed by the model was 11.49 mL with optimum inoculum concentration at 10 %, pH of 5, 18°Brix of sugar concentration, 28 °C of temperature at 42 h. All factor variables evaluated had a significant effect on the bioethanol production with probability less than 0.05. The bioethanol has a potential to be used as solid fuel, and furthermore, ethanol yield may have inhibitory impact on the fermentation microorganisms hence lowering product formation.