Volumetric oxygen transfer coefficient as a means of improving volumetric ethanol productivity and a criterion for scaling up ethanol production with Escherichia coli

BACKGROUND: This study evaluated the influence of different micro-aerated conditions, including the aeration rate, the volumetric oxygen transfer coefficient (k_La) and the oxygen transfer rate (OTR), on improving ethanol productivity and scale-up of the fermentation step of the ethanologenic Escherichia coli strain MS04 in mineral medium supplemented with xylose, glucose, and sodium acetate. RESULTS: Growth and ethanol production results using 0.75 L of fermenter showed that micro-aeration (0.1 vvm, 400 rpm) improved the volumetric ethanol productivity and sugar consumption rate compared with the anaerobic condition (0 vvm, 400 rpm) or higher aeration rates (>0.2 vvm) without reducing significantly the ethanol yield. The k_La and the OTR were estimated and a k_La value of 7.2 h⁻¹ was used as a criterion to scale-up the fermentation process from 0.75 L to 9.16 L and 110 L. During scale-up, the volumetric ethanol productivity and ethanol yield of consumed sugars were maintained at similar levels to those obtained in the laboratory in the 0.75 L fermenter. CONCLUSIONS: The controlled supply of low levels of oxygen promoted an increase in the concentration of biomass favoring the production and volumetric productivity of ethanol. The use of k_La allowed the fermentation step to be scaled up with ethanologenic E. coli maintaining similar ethanol yields and productivities.