Continuous ethanol production from sugar beet molasses using an osmotolerant mutant strain of Zymomonas mobilis

Abstract

Abstract A laboratory process was established for ethanol production by fermentation of sugar beet molasses with the bacterium Zymomonas mobilis . Sucrose in the molasses was hydrolyzed enzymatically to prevent levan formation. A continuous system was adopted to reduce sorbitol formation and a two-stage fermentor was used to enhance sugar conversion and the final ethanol concentration. This two-stage fermentor operated stably for as long as 18 d. An ethanol concentration of 59.9 g/ l was obtained at 97% sugar conversion and at high ethanol yield (0.48 g/g, 94% of theoretical). The volumetric ethanol productivity (3.0 g/ l ·h) was superior to that of batch fermentation but inferior to that of a single-stage continuous system with the same medium. However, the thanol concentration was increased to a level acceptable for economical recovery. The process proposed in this paper is the first report of successful fermentation of sugar beet molasses in the continuous mode using the bacterium Z. mobilis .