High Cell Density Lactic Acid Fermentation with Cell Recycle Bioreactor

With the increasing usage of lactic acid in food, pharmaceutical and polymer industries, high productivity lactic acid fermentation is gaining considerable attention. The main limitations of conventional fermentation systems, lower productivity due to low cell density and product inhibition, can be overcome by the use of membrane recycle bioreactors. A comparative study of the lactic acid fermentation in a continuous flow bioreactor with and without cell recycle is presented. The fermentation carried out using Lactobacillus rhamnosus NRRL B445 with relatively high concentrations of glucose (100 g/L) is described. Polyolefin microfiltration membrane of 0.1 μm pore size (area = 0.1 m2) is used for cell recycle. The filtration characteristics of culture broth with the membrane are studied initially to evaluate the effects of process parameters. The fermentation is studied at two different dilution rates. It is pointed out that cell density as high as 130-145 g/L could be achieved in recycle mode which is 15-30 times higher than the conventional mode. The productivity of 34.77 g/L h with cell recycle at a dilution rate of 0.409 h-1, is three times higher than without recycle. The substrate conversion and the production concentration are higher with cell recycle at both the dilution rates. A significant decrease in the membrane flux due to high cell density could be noticed after 80-90 hours of fermentation with recycle.