Application Of Advanced On-line Sensors In Fuel Ethanol Fermentation And Optimization Of Fermentation Process

Due to the consumption of fossil fuels and a series of environmental and energy problems brought by fossil fuels,fuel ethanol is the most widely used biofuel.However,the production of fuel ethanol still has disadvantages in terms of economy.Therefore,the development of efficient ethanol fermentation technology is the key to achieve low cost production.In this research,ethanol fermentation by Saccharomyces cerevisiae was taken as the object.The key factors including the medium,process monitoring and control strategy were systematically optimized.Through the integrated analysis of intracellular metabolite map,key enzyme activity and metabolic flux,the carbon source supplement strategy was further studied.Thus,the regulation between ethanol and glycerol was analyzed to provide theoretical guidance for the development of efficient process strategies.Firstly,response surface methodology(RSM)was used to optimize the fermentation medium components and operating conditions for ethanol production by S.cerevisiae.Through single factor experiment(a),Plackett-Burman experiment(b),steepest climb experiment(c),central composite experiment design and experimental verification(d),it was found that glucose,inoculation and yeast extract amount were the three most important factors affecting ethanol yield.When the glucose concentration was 285.0 g/L,the inoculation amount was 29%,and the yeast extract concentration was 16.5 g/L,the ethanol production concentration of shaking flask fermentation could achieve 124.4±0.8 g/L,which was 32.2%higher than original condition(94.1±1.7 g/L).Secondly,advanced on-line sensors such as electronic nose and viable cell sensor were introduced into the ethanol fermentation process.An online detection method was established for the determination of key indexes such as ethanol concentration and living cell concentration in fermentation process.The correlation between the ethanol concentration detected by electronic nose and by HPLC and the correlation between the capacitance value detected by viable cell sensor and colony forming unit(CFU)detected off-line reached 0.999 and 0.996,respectively.On this basis,the application of viable cell sensor and electronic nose in the regulation of online glucose supplementation strategy could effectively alleviate the inhibition of initial high glucose concentration on the growth and metabolism of S.cerevisiae,and the ethanol production,productivity and yield of ethanol were increased by 15.4%,15.9%and 9.0%,respectively.Finally,pH control,oxygen supply level and glucose supplement strategy of ethanol fermentation were researched on 5 L bioreactor.The results showed that natural pH,0.5 vvm and the strategy of stage glucose supplementation could increase ethanol production and productivity to 138.2 g/L and 5.76 g/L/h,and reduce the glycerol by 41.7%.To further study the effect of step-wise glucose feeding strategy,the intracellular metabolite map,key enzyme activities and intracellular metabolic flux were integratedly analyzed.The improvement of ethanol production efficiency under the strategy of glucose supplementation is attributed to the enhancement of cell metabolic capacity and the improvement of glucose conversion.In addition,higher intracellular redox status and reduced activity of key enzymes in the glycerol synthesis pathway are the main reasons for the significant decrease in glycerol content,which leads to more carbon flowing to ethanol synthesis.