Application of a membrane recycle bioreactor for continuous ethanol production

Summary 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·1^–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·1^–1·h^–1) was attained at an ethanol concentration of 81 g·1^–1. The highest demands of cells for maintenance energy were found at the maximum feed substrate concentration (300 g·1^–1) and at very low concentrations of cells in the broth.