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(L)a) 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(L)a and the OTR were estimated and a k(L)a 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(L)a allowed the fermentation step to be scaled up with ethanologenic E. coli maintaining similar ethanol yields and productivities. (C) 2016 Society of Chemical Industry