APPLICATION OF A MEMBRANE RECYCLE BIOREACTOR FOR CONTINUOUS ETHANOL-PRODUCTION

A series of continuous fermentations were carried out with a production strain of the yeast Saccharomyces cerevisiae in a membrane bioreactor. A membrane separation module composed of ultrafiltration tubular membranes retained all biomass in a fermentation zone of the bioreactor and allowed continuous removal of fermentation products into a cell-free permeate. In a system with total (100%) cell recycle the impact of fermentation conditions [dilution rate (0.03-0.3 h-1); substrate concentration in the feed (50-300 g.l-1); biomass concentration (depending on the experimental conditions)] was studied on the behaviour of the "immobilized" cell population and on ethanol formation. Maximum ethanol productivity (15 g.l-1.h-1) was attained at an ethanol concentration of 81 g.l-1. The highest demands of cells for maintenance energy were found at the maximum feed substrate concentration (300 g.l-1 and at very low concentrations of cells in the broth.