Ethanol production by 'Zymomonas mobilis' CP4 under chemostatic and continuous transient reactor operation

Abstract

Ethanol production by Zymomonas mobilis CP4 under chemostatic and continuous transient reactor. Ethanol production by Zymomonas mobilis CP4 under chemostat and continuous transient operation has been investigated. Under carbon limitation with simple chemostatic operation, glucose, fructose and sucrose were tested at 35° C. At 2%(w/v) carbon source medium, glucose was more efficiently utilised. Ethanol production values for glucose, fructose and sucrose were respectively; volumetric productivity 2.5, 1.8 and 2.5 g/1/h; conversion to ethanol efficiency 96, 88 and 76% at values of dilution rate of 0.35, 0.21 and 0.32 h-1 which represent approximately 85% of Dm. With 5%(w/v) glucose values of volumetric productivity of 5 g/l/h and conversion to ethanol efficiency of 85% were achieved. However, under nitrogen limitation with glucose 5% (w/v), approximately 25% of feed glucose medium was being washed out while conversion to ethanol efficiency was around 60% at a dilution rate of 0.17 h-1 Under alternating glucose concentrations of 2 and 5%(w/v) medium and at a fixed dilution rate of 0.2 h-1, continuous transient operation achieved values of ethanol conversion higher than 80%. However, both continuous transient (utilising high alternating glucose concentration of 8 and 11% and 8 and 16%(w/v)) and simple chemostatic operation running with 9.5 and 12%(w/v) glucose medium were less satisfactory as conversion efficiency values were as less satisfactory as conversion efficiency values were as low as 40 and 29% for the former and 48 and 45% for the 1atter. Pulsing the culture with mineral salts (NH+4, Mg++,K+) and ethanol, the culture showed no effect with mineral salts and a strong inhibitory effect on growth for ethanol.