Ethanol from whey: Continuous fermentation with cell recycle

The production of ethanol from cheese whey lactose has been demonstrated using a single-stage continuous culture fermentation with 100% cell recycle. In a two-step process, an aerobic fed batch operation was used initially to allow biomass buildup in the absence of inhibitory ethanol concentrations. In the anaerobic ethanol-producing second step, a strain of Kluyveromyces fragilis selected on the basis of batch fermentation data had a maximum productivity of 7.1 g ethanol/L/h at a dilution rate of 0.15 h(-1), while achieving the goal of zero residual sugar concentration. The fermentation productivity diminished when the feed sugar concentation exceeded 120 g/L despite the inclusion of a lipid mixture previous shown to enhance batch fermentation productivities.