Application of oscillation for efficiency improvement of continuous ethanol fermentation with Saccharomyces cerevisiae under very-high-gravity conditions

Compared with steady state, oscillation in continuous very-high-gravity ethanol fermentation with Saccharomyces cerevisiae improved process productivity, which was thus introduced for the fermentation system composed of a tank fermentor followed by four-stage packed tubular bioreactors. When the very-high-gravity medium containing 280 g l(-1) glucose was fed at the dilution rate of 0.04 h(-1), the average ethanol of 15.8% (v/v) and residual glucose of 1.5 g l(-1) were achieved under the oscillatory state, with an average ethanol productivity of 2.14 g h(-1) l(-1). By contrast, only 14.8% (v/v) ethanol was achieved under the steady state at the same dilution rate, and the residual glucose was as high as 17.1 g l(-1), with an ethanol productivity of 2.00 g h(-1) l(-1), indicating a 7% improvement under the oscillatory state. When the fermentation system was operated under the steady state at the dilution rate of 0.027 h(-1) to extend the average fermentation time to 88 h from 59 h, the ethanol concentration increased slightly to 15.4% (v/v) and residual glucose decreased to 7.3 g l(-1), correspondingly, but the ethanol productivity was decreased drastically to 1.43 g h(-1) l(-1), indicating a 48% improvement under the oscillatory state at the dilution rate of 0.04 h(-1).