PRODUCTION OF 1,3-PROPANEDIOL BY CLOSTRIDIUM-BUTYRICUM IN CONTINUOUS-CULTURE WITH CELL RECYCLING

The continuous fermentation of 1,3-propanediol from glycerol by Clostr idium butyricum was subjected to cell recycling by filtration using ho llow-fibre modules made from polysulphone. The performance of the cult ure system was checked at a retention ratio (dilution rate/bleed rate) of 5, dilution rates between 0.2 h(-1) and 1.0 h(-1) and glycerol inp ut concentrations of 32 g l(-1) and 56 g l(-1). The near-to-optimum pr opanediol concentration of 26.5 g l(-1) (for 56 g l(-1) glycerol) was maintained up to a dilution rate of 0.5 h(-1) and then decreased while the propanediol productivity was highest at 0.7 h(-1). The productivi ty could be increased by a factor of four in comparison to the continu ous culture without cell recycling. By application of the model of Zen g and Deckwer [(1995) Biotechnol Prog 11: 71-79] for cultures under su bstrate excess, it was shown that the limitations resulted exclusively from product inhibition and detrimental influences from the cell recy cling system, such as shear stress, were not involved.