Studies On Continuous Ethanol Fermentation With Recycling Of Distillage And Impact Of By-products On Growth And Ethanol Fermentation Of The Self-flocculating Yeast SPSC01

The recycling of distillage produced by industrial fermentation may help to reduce its environmental impact, and limit waste water emission. However, we have found that the recycling of distillage causes a significant reduction in the fermentation efficiency. The effluents generated from industrial fermentations therefore need to be treated before reuse.Continuous fuel ethanol fermentation technology using the yeast SPSC01 has been successfully developed. SPSC01 is a self-flocculating yeast, and this property has greatly facilitated its separation from the product after fermentation.In this paper, continuous ethanol fermentations by SPSC01 with recycling of distillage were carried out in a single-stage bioreactor using two-stage enzymatic hydrolyte of corn powder as a medium. Through coupling fermentation with the recycling of distillage, it was found that the untreated distillage exerted a significant inhibition on the process of fermentation. Analysis of the metabolic pathways associated with ethanol fermentation revealed several by-products with high boiling points contained within the waste distillage discharged from the fermentation. HPLC analysis showed that these by-products include acetic, propionic, and lactic acids, furfural and 2-phenyl-ethyl-alcohol. The concentrations of these by-products accumulated in the distillage with increasing number of recycling. The effects of these by-products on the growth of SPSC01 and ethanol fermentation were investigated by adding these by-products into the fermentation system. The result indicated that the minimum inhibitory concentration of acetic, lactic, and propionic acids, furfural and 2-phenyl-ethyl-alcohol on the growth of SPSC01 were 3 g/L,20 g/L,1.5 g/L,2 g/L,1.5 g/L, respectively, and that these by-products also worked in synergism. These by-products could be removed from the distillage through adsorption by hydrophobic polymeric adsorbents in sequence (D-101 followed by D-301), resulting in a final adsorption efficiency of 70.09%, 55.76%,82.99%,84.50%,70.86%,59.44%and 98.75%for acetic, propionic, and lactic acids, furfural,5-HMF,2-phenyl-ethyl-alcohol and pigment were, respectively.We have established a material balance for the repeated use of fermentation effluents, by which the theoretical, feasible and economical potentials have been analyzed to provide a theoretical basis for reducing industrial waste water, and hence sewage output, and making the best use of the nutrients in the effluents for the fermentation industry.