Ethanol Fermentation From Sugarcane Molasses By Self-Flocculating Yeast Strain SPSC01

In the process of bio-ethanol fermentation using molasses,one of its characteristics is that molasses can be easily implement cleaned-liquid fermentation,combine which with the self-fixation capability of self-flocculating yeast strain will predigest the flowing unit operation such as separation or rectification.In this work,the process of bio-ethanol production by fermentation of sugarcane molasses was investigated to explore the feasibility of this process in the industrial-scale application.The self-flocculating yeast strain SPSC01 and other three yeast strains from our laboratory were tested for their abilities to ferment sugarcane molasses.The results showed that SPSC01 achieved the highest performance yielding the highest ethanol concentration and lowest reducing sugar concentration.Using Uniform Design principles,the conditions for molasses fermentation by SPSC01 were optimized by addition of nitrogen(0.3 g L^-1) and phosphorous(0.3 g L^-1) and 0.6%(v/v) corn steep liquor,and the ratio of brown sugar to molasses was kept at 7:3(w/w).Under these conditions,the total reducing sugar concentration was reduced by 46.2%,ethanol and maximum biomass concentrations were increased by 10.2%and 92.1%,respectively,and the total fermentation time was reduced by 33.3%relative control(without nitrogen,phosphorous and corn steep liquor).This resulted in a productivity improvement of 65.5%.Metabolic flux analysis indicated that the changes in the distribution of carbon flux were due to the result of an increase in the number of yeast cells during fermentation,and not an increase in the fermentation efficiency of individual cells.A bio-reactor system composed of four fermentors in series was used to simulate the process of industrial-scale fermentation.Under the optimized conditions,the total reducing sugar concentration of the culture in the system was maintained 7 g L^-1,while ethanol concentration was kept above 88 gL^-1,and biomass at 12g L^-1.The ethanol productivity of the entire system was calculated to be 3.96 g L^-1 h^-1.In the fourth fermentor of this system,the size of the self-flocculating yeast was monitored by Focused Beam Reflectance Measurement (FBRM) technique.The mean square weighted value of SPSC01 was 270μm.The ethanol productivity of the optimized culture increased by 55.3%compared to control.The average chord length of yeast particles also increased by 68.8%.The data showed that it is feasible to apply this process to bioethanol production at the industrial-scale.Finally,a method for the disposal of waste distillage during molasses was investigated. Under the conditions described in this study,the waste distillage could be completely recycled in the system,but this would lead to inhibition of the fermentation performance of SPSC01. The results of additional tests indicated that the metabolites did not reach the concentrations that have inhibitory effect.The main restrictive factors have yet to be established and still require further study.