Process optimization for very high concentration ethanol fermentation by self-flocculating yeast

In this work, to improve ethanol fermentation based on 300 g·L^-1 initial glucose, the statistical approaches were employed to optimize the fermentation conditions. Plackett-Burman design was used for the initial screening, and (NH₁SO₄, KH₂PO₄ and inoculum size were identified to be the significant variables. The three variables were chosen for further optimization by central composite design of the response surface methodology. The optimal conditions were eventually determined to be 16.8 g·L^-1 (NH₄)₂SO₄, 8.24 g·L^-1 KH₂PO₄ and 11.25% of inoculum size, which were experimentally validated and led to a final level of 137.7 g·L^-1 ethanol in fermentation broth, representing approximately 28% increase in comparison with 107.5 g·L^-1 ethanol of the control obtained under non-optimization conditions. Simultaneously, under the optimal conditions, the fermentation time was shorten from 72 to 60 h, thus ethanol production rate was significantly elevated from 1.49 to 2.29 g·L^-1·h^-1.