Multi Kettle Series Of Self-flocculating Yeast Ethanol Continuous Fermentation Bioreactor System

A bioreactor system composed of multi-stage tank fermentors in series was established, in which a self-flocculating yeast strain developed by protoplast fusion technology was applied to ferment corn powder two-stage enzymatic hydrolyzate to produce ethanol.Firstly, a seed fermentor was coupled into the fermentation system composed of three tanks in series, and the hydrolyzate medium containing reducing sugar 100 g/L, added 2.0g/L (NH4)2HPO4 and KH2PO4, respectively, was fed into the seed fermentor at the dilution rate of 0.017h~' for the self-flocculating yeast seed cultivation. Meanwhile, the hydrolyzate medium containing reducing sugar 220 g/L, added 1.5g/L (NH4)2HPO4 and 2.5g/L KH2PO4) was fed into the first fermentor at the dilution rates of 0.017, 0.025, 0.033, 0.040 and 0.050 h-1, respectively. The experimental results showed that Chemostat states were developed for seed cultivation and ethanol fermentations under the dilution rates of 0.017, 0.025, 0.033 and 0.050 h-1. However, the oscillations of fermented parameters, including residual sugar, ethanol and biomass concentrations, were observed under the dilution rate of 0.040 h-1 for this continuous ethanol fermentation system. Over 12% (v/v) ethanol was achieved, at the same time, residual reducing sugar and total sugar were maintained below 0.15% and 0.35% (w/v) when the dilution rate was controlled no more than 0.033 h-1. The ethanol productivity of the entire fermentation system was calculated to be 2.71g/(L-h).Secondly, the seed fermentor was removed from the above bioreactor syatem, and the yeast floes grown inside fermentors were used to support ethanol fermentation. Using same ferment medium, over 13% (v/v) ethanol was achieved, at the same time, residual reducing sugar and total sugar were maintained below 0.30% and 0.40% (w/v) when the dilution rate was controlled no more than 0.040 h-1. The ethanol productivity of the entire fermentation system was calculated to be 3.47g/(L-h). These experimental running indicated that this new ethanol fermentation technology using self-flocculating yeast cells can be applied to such a fermentation system composed of tanks in series that was widely used in ethanol fermentation industry in China at present and help improve its efficiency and save production cost.Finally, the effect of the complete recycling use of distilled effluent on ethanol fermentation was examined in order to save the cost for the treatment of waste distillage and promote cleansing production. Based on the data of 13 circulations, although the average fermentation time needed to be extended to 30~40 hours, over 12.5% (v/v) ethanol was achieved, at the same time, residual reducing sugar and total sugar were maintained below 0.70% and 0.90% (w/v), which indicates that the negative effect of the completely recycling use of waste distillage was limited, and the waste distillage can be completely recycled within the fermentation system.