A pilot-scale study of ethanol production by mixed culture of Saccharomyces cerevisiae M30 and Kluyveromyces marxianus DMKU 3-1042 in a packed-bed reactor

Abstract

A renewable energy, ethanol earns more interest because of its benefits such as clean energy and production from biomass fermentation. As Thailand is located in the tropics, sugarcane has the potential to serve as an important carbon source. Moreover, ethanol fermentation at high temperature has received much attention for effective ethanol production since average day-time temperatures are usually high throughout the year. The advantages of ethanol fermentation at high temperature are reduced in cooling costs and decreased risk of contamination. Hence, in the present work, ethanol fermentations using thermotolerant yeast, Kluyveromyces marxianus DMKU 3-1042 and Saccharomyces cerevisiae M30 in monoculture and mixed cultures were studied. The cultures in forms of suspended cells and immobilized cells adsorption on the fibrous of thin shell silk cocoon (TSSC) were used for the investigation with dark brown sugar as a carbon source at the initial sugar concentration of 220 g/l. The ethanol fermentation by the mixed culture system using TSSC as a carrier was found to be the most effective system. Under batch fermentation in 500 ml Erlenmeyer shaking-flasks, the immobilized mixed culture system was capable of highly efficient ethanol production at various temperatures (33-40℃).Under uncontrolled temperature condition in 1-L continuous packed-bed reactor using the mixed culture immobilized on TSSC, the highest productivity (16.55 g/L h) was obtained at 0.40 h⁻¹ of dilution rate with ethanol concentration of 41.86 g/L, whereas, the maximum of ethanol concentration (70.95 g/L) was obtained at 0.10 h⁻¹ of dilution rate The immobilized mixed culture on TSSC was promising for continuous fermentation process under uncontrolled operating temperature. Moreover the continuous ethanol production was excellently performed carried out in a 100-L packed bed, at the dilution rate of 0.1 h⁻¹ with the ethanol concentration and productivity were 85.34±3.00 g/L and 8.53 g/L h, respectively.