Kinetics of continuous ethanol production by Zymomonas mobilis on sugar cane molasses

Kinetics parameters on sugar cane molasses were analyzed under different experimental conditions using Zymomonas mobilis CP4 in continuous culture. The effect of the dilution rate at molasses medium concentration of 100 and 135 g/L, molasses concentration at dilution rate of 0.17 h-1 and fermentation temperature at dilution rate of 0.17 h-1 were studied. At a dilution rate of 0.28 h-1 the ethanol productivity, yield and concentration respectively were 8.3 g/L.h, 0.42 g/g and 30 g/L with 100 g/L molasses medium concentration. At molasses medium concentration of 135 g/L, at a dilution rate of 0.23 h-1, the ethanol concentration reached 33 g/L giving 85% sugar conversion and ethanol productivity of 7.4 g/L.h. In both cases the ethanol yield was over 80% of the theoretical value. The maintenance energy coefficient (m) was relatively high and was calculated as 2.89 and 5.59 g/g.h for 100 and 135 g/L molasses medium concentration respectively. The kinetics parameters: were affected negatively only when the molasses medium concentration was upper than 135 g/L. Under our conditions, the fermentation could be run from 30 to 35 degrees C without any change in kinetics and yield parameters.