Self-flocculating Yeast Alcoholic Continuous Fermentation And Cogeneration Yeast Process

When the specific growth rate u, residual sugar level S and biomass concentration X were designated to be the target function, respectively, the high density cultivation of a self-flocculating yeast strain, SPSC01, a fusant from Saccharomyces cerevisiae and Schizosaccharomyces pombe, was investigated in a laboratory scale airlift suspended-bed bioreactor using uniform design strategy and its corresponding software UD3.0, developed by Prof. Kaitai Fang, Chinese Mathematics Association. The cultivation parameters were optimized. The cultivation temperature should be controlled at 30℃, whereas the airflow rate 0.012vvm and the medium composed of sugar 220g/L, corn steep liquor .4g/L and (NH4)2HPO4 3.0g/L. These optimized cultivation parameters were validated experimentally and a yeast cell density as high as 18g(d.w)/L was achieved when the medium was fed at a dilution rate of 0.02 h-1.Then, an ethanol fermentation system composed of three/four laboratory scale airlift suspended-bed bioreactor in series and with a total working volume of 4800 ml was established and continuous ethanol fermentation coupled with the production of yeast was carried out experimentally. When the dilution rate based on the total working volume of the bioreactor system was controlled at 0.05 h-1, an average ethanol concentration of 12% (v/v), together with residual sugar level of 5 g/L and 10 g/L for reducing and total ones, respectively, was achieved. At the same time, 18.4g (d.w) yeast was produced daily and this amount of yeast was calculated to be 5% of ethanol produced over a period of 30 days' running.