An internal filter feedback system with a stainless steel filter was introduced and its application on the continuous ethanol fermentation was studied.
Flux with a stainless steel filter was highly dependent on the agitation speed in a fermentor. Retention coefficient with an internal stainless steel filter of 2μm pore size was found to be more than 97.5%.
Ethanol fermentation of Saccharomyces cerevisiae was carried out and maximum cell concentration up to 157g-dry wt/L was obtained. However best operable cell concentration was between 90 and 150g-dry wt/L. The cell concentration in the fermentor was maintained by proper manipulation of dilution rate and bleed ratio with the growth rate. Ethanol productivity and yeast output rate at steady state increased as the bleed ratio decreased above a certain dilution rate. There exists an optimum value of dilution rate for maximum ethanol productivity. The ethanol productivity with a feeding substrate concentration of 100g/L was 41g/L-h at steady state. The actual ethanol yield was 92.7% of the theoretical yield.
This study shows that the internal filter feedback system with a stainless steel filter can be as successful as external cell recycle systems for high density cell culture and ethanol fermentation. Furthermore, it can be scale up more easily than external cell recycle systems.
