Study On Producing Ethanol By Zymomonas Mobilis

With the development of society, fossil fuels is being used up and environmental issues are getting worse, new energy development has been become the focus of national concern. Fuel ethanol is a clean, renewable and sustainable biomass fuel, which has low-carbon, low emission and other characteristics. It can be used as alternative to fossil fuels. So far, many countries are interested in the development of ethanol, it will become an integral part of the world energy consumption.This paper is based on using Zymomonas mobilis as a producing strain, and apple pomace as raw materials for ethanol fermentation. First of all, Zymomonas mobilis ZM607 was screened out from the natural environment; then, fermentation conditions and medium were optimized; finally, the optimum process parameters of ethanol fermentation with apple pomace as raw materials was studied.The main results of this paper are as follows:(1) Strain ZM607 was isolated from soil and identified as Zymomonas mobilis by 16S rDNA, the yield of ethanol was 41.1g/L.(2) The single-factor experiment and response surface methodology were employed to optimize the fermentation conditions and medium for ethanol produced by strain ZM607. The factors which influence ethanol yield (glucose concentration, yeast concentration, pH, temperature, inoculum size, and other basic ingredients) were figured out by single-factor experiment. On the basis, Plackett-Burman design was employed to evaluate the effects of eight factors, the results of which showed that glucose, yeast powder, and temperature were main affecting variables of ethanol yield. Then steepest ascent method was used to approach their maximum response regions, followed by Box-Behnken design and response surface analysis, to determine the optimal value of significant factors. The optimum fermentation medium and conditions were as follows: glucose 164.4g/L, yeast powder 8.2g/L, temperature was 27 ℃, KH2PO4 1g/L, MgSO4·7H2O 0.5g/L, (NH4)2SO4 1g/L, pH was 7, inoculum size was 5%. Under the optimized conditions, the final yield of ethanol reached up to 67.9g/L and was 65.2% higher than before the optimization.(3) The single-factor and orthogonal experiments were used to find out the optimum pretreatment conditions of apple pomace. Firstly, the change rate of content of reducing sugar was 142.8% after acid hydrolysis for 20min under pH was 1 and temperature was 121 ℃. And then apple pomace was treated by cellulase enzymolysis and pectinase enzymolysis. The optimum enzymolysis conditions were addition amount of cellulase 0.9%(substrate weight), addition amount of pectinase 0.25%(substrate weight), reaction emperature 40 ℃, pH 4.5, time of enzymolysis 12h. When we used the two steps above to pretreat the apple pomace, the yield of reducing sugar reached up to 307.1g/kg. Finally, the optimum fermentation conditions of apple pomace saccharification liquid for producing ethanol was studied, the results were as follows:the medium was supplemented with 8.2g/L yeast powder, lg/L KH2PO4,0.5g/L MgSO4-7H2O, lg/L (NH4)2SO4, fermentation temperature was 28 ℃, initial pH of fermentation medium was 6.0, inoculum size was 5%, time of fermentation was 3 days. Under this optimal contions, the final yield of ethanol reached up to 156.8mL/kg.