The Study Of Bio-ethonol Production Under Redox Potential Control Condition

Biofuels can effectively reduce human dependence on oil resource. As the most important biofuel, ethanol still faces many problems in industrial production such as high energy cost and high feedstock cost. The application of very high gravity technique and using lignocellulosic materials are ideal ways to meet the economic process, in which the redox potential (also known as ORP) control can be more helpful due to its effects on cell metabolic flux and improvement of cell stress tolerance.Very high gravity ethanol fermentation benefits the energy saving, and with the ORP control in such continuous process, the cell metabolism were very different. As illustrated by the results, under the feeding of 100 g/L glucose, the ORP value for nonaeration and aeration were close (-152 to-137 mV), thus the final ethanol did not change (around 38 g/L). As long as the feeding glucose increased to 200 and 300 g/L, the ORP value of aeration was about 25-30 mV higher than nonaeration, which caused the ethanol improved by 15%and 81%, respectively. For very high gravity condition (300 g/L), ethanol yield and ethanol productivity were all higher than those of 200 g/L.Lignocellulosic biomass for ethanol production was a kind of sustainable choice. However, some inhibitors such as acetic acid were harmful to yeast cell. When ORP control used, cells performed better tolerance and detoxification. The results showed that the addition of acetic acid reduced the biomass from 5.4 g/L (blank) to 0.38 g/L (5 g/L acetic acid), but distribution of metabolites was not changed. The high ORP, also called oxidation state, im-proved the yeast fermentation and removed the acetic acid from-0.179-0.007 to 0.167 0.304 (detoxification).ORP control did not only improve the very high gravity ethanol fermentation during continuous process, but also enhanced the tolerance and detoxification to inhibitors during lignocellulosic biomass fermentation. Therefore, ORP control owned an optimistic prospect on ethanol industry in the future.