The Effect of Oxygen Transfer Rate on Continuous Ethanol Fermentation by Kluyveromyces marxianus
Catherine J. Hack*, R. Marchanl
Biotechnology Research Group, University of Ulster at Coleraine, Cromore Road, Co. Londonderry, Northern Ireland, 11T52 1SA, UK.
Received October 17, 1995
Accepted December 6, 1995
The effect of oxygen transfer rate on the growth rate, the specific ethanol productivity and the volumetric elhanol productivity of the thermotolerant yeast Kluyveromyces marxianus ÌMB3 in a continuous ethanol fermentation was investigated. Under anaerobic conditions the strain grew poorly, with a maximum biomass concentral ion of 0.4 g L-1. A small increase in oxygen transfer to the culture led to an increase in both the specific growth rate and the specific ethanol productivity. Further increases in the oxygen transfer rate to the culture caused a linear increase in the growth rate but a rapid decrease in the specific elhanol productivity. The specific ethanol productivity decreased to a constant minimum value of 0.25 (±0.05) g ethanol (g cells h)-1. An initial maximum volumetric elhanol productivity, 0.14 g L-1 was achieved at an oxygen transfer rate to the culture broth of 3 mmol L-1h-1. The volumetric elhanol productivity increased again as the biomass concentration continued to rise although the specific elhanol productivity had levelled, reaching a maximum of 0.44 g L-1h-1. The biomass concentration in a non-aerated chemostat was estimated using the cell yield on oxygen and the oxygen transfer rate to the broth.