Improving The Production Of Fermentative Ethanol And Optimizing The Fermentation Process With Wheat Straw

The use of lignocellulose to produce fuel ethanol,also known as cellulosic ethanol,is an effective way to alleviate environmental and energy problems,and it has been the focus of researchers.At present,cellulosic ethanol fermentation still faces some problems that hinder its large-scale production and application.These problems include incomplete straw pre-treatment with high cost,and producing molecules such as acids,aldehydes and phenols harmful to fermentation.During the fermentation process,it is difficult to use both six-carbon and five-carbon sugars simultaneously,and difficult to control the fermentation process of high solids in fermentation broth.This research takes wheat straw as the research object,and intends to explore the aspects of raw material pre-treatment,improve the tolerance of yeast to pre-treatment toxic and side substances and optimize the fermentation process of cellulosic ethanol for improved cellulosic ethanol production.Firstly,the treatment process of wheat straw with a combination of Na OH and dilute sulfuric acid was optimized.After a pre-treatment with 1.5% Na OH and 2%dilute sulfuric acid,cellulase was used for enzymatic hydrolysis with the initial p H of5.0,the reaction temperature of 45°C,and the enzyme dosage of 35 FPU/g.The final glucose concentration reached 47.8 g/L,the xylose concentration 22.2 g/L,and the arabinose concentration 3.74 g/L.Secondly,during the preparation of straw hydrolysate,many inhibitors will be produced,of which furfural has a strong inhibitory effect on yeast ethanol production.In this study,the glutamine synthetase gene GLN1 of Saccharomyces cerevisiae was inserted into vector p ESC-URA,which was introduced into the original yeast BY4741 to construct the recombinant yeast YEA9.The furfural tolerance and fermentation performance of both YEA9 and BY4741 were then measured.The results showed that in a medium with a furfural concentration of 1.55 g/L,the biomass of YEA9 increased by 3.7 times compared to BY4741,the sugar consumption rate increased by 8.6 times,the final ethanol content increased by 9.2 times,and the conversion rate of sugar alcohol increased by 10.6 %,respectively;in the simulated hydrolysate with a furfural concentration of 1.10 g/L,the biomass of YEA9 increased by 1.75 times compared to BY4741,the sugar consumption rate increased by 6.1 times,the final ethanol content is increased by 5.3 times,and the sugar alcohol conversion rate is increased by 0.5 %.Finally,the fermentation processes using stepwise saccharification and simultaneous saccharification of the recombinant strain YEA9 were compared.During the stepwise saccharification and fermentation process,the temperature of the fermentation was 30°C,the initial p H value was 4.5,and the inoculation amount was5%,while the reaction temperature of simultaneous saccharification and fermentation was 38.5?,the initial p H value was 4.5,and the inoculation amount was 5%..The results showed that after the stepwise saccharification and fermentation,the ethanolcontent in the fermentor was 23.2 g/L,and the ethanol content after the simultaneous saccharification and fermentation was 20.3 g/L.This study improves the ability of Saccharomyces cerevisiae to produce ethanol in straw hydrolysate,which would promote the development of cellulosic ethanol production technology.