The effect of pH, temperature and sucrose concentration on high productivity continuous ethanol fermentation using Zymomonas mobilis

Abstract

A flocculent strain of Zymomonas mobilis was used for ethanol production from sucrose. Using a fermentor with cell recycle (internal and external settler) high sugar conversion and ethanol productivity were obtained. At a dilution rate of 0.5 h-1 (giving 96% sugar conversion) the ethanol productivity, yield and concentrations respectively were 20 g/l/h, 0.45 g/g and 40 g/l using a medium containing 100 g/l sucrose. At a sucrose concentration of 150 g/l, the ethanol concentration reached 60 g/l. The ethanol yield was 80% theoretical due to levan and fructo-oligomer formation. No sorbitol was detected. This fermentation was conducted at a range of conditions from 30 to 36°C and from pH 4.0 to 5.5.