Pretreatment Of Corn Stover By White Rot Fungi And Optimization Of Ethanol Production Process By Mixed Yeast

Corn stover,a typical lignocellulosic biomass material,can not only solve the energy crisis but also reduce environmental pollution.This study used fungal pretreatment to degrade the lignin in corn stover,selected the best degrading strains,compared the different methods of enzymatic saccharification and the fermenting ability of yeast species,and finally optimized the process of converting hydrolysis to ethanol.The main results are as follows:1.Six fungi were evaluated according to their ability of producing lignocellulosic hydrolase,component of corn stover,the degradation rate and selectivity index after pretreated.The results showed that C.gallica,T.versicolor,P.sajor-caju grew fast in corn stover and their selectivity index was greater than 1 during the pretreatment.At the same time,the highest activity levels of laccase and manganese peroxidase were 29.22 and 10.22 U g^-1 dry biomass for T.versicolor at 25 days,much higher than other fungi?p<0.05?.Among six fungi,the lowest lignin content was 19.05%?p<0.05?,cellulose content was 43.10%and hemicellulose content was 24.64%for P.sajor-caju at 25 days.The most dry matter loss fell in C.gallica?p<0.05?,also its degradation of lignin and cellulose was high.2.Adding different crude enzyme solution obtained by C.gallica,T.versicolor,P.sajor-caju during pretreatment in the medium that producing the cellulase and xylanase for T.reesei and then comparing the above method with traditional enzymatic saccharification using the commercial enzymes was studied.This study showed that the cellulase activity decreased and the xylanase activity increased when added in crude enzyme solution.Using commercial enzymes to hydrolyze corn stover is still the best way and the concentration of reducing sugar can reach up to 28.13 g/L,which was significantly higher than saccharification in situ with cellulase and xylanase produced by T.reesei?p<0.01?.Moreover,the surface pores were enlarged,the amorphous area of the stover was degraded and the strong of bond relating with lignin was decreased and obtained the highest sugar concentration?p<0.05?after P.sajor-caju25 days pretreatment for corn stover.3.The ability of using glucose and xylose for C.utilis and P.stipites was studied.The results showed that the ability of C.utilis converting glucose to ethanol was better.It could convert 20 g/L glucose to 9.04 g/L ethanol within 12 h.P.stipites converting xylose to ethanol was better.It could convert 20 g/L xylose to 8.19 g/L ethanol within 48 h.When fermenting glucose and xylose mixture,it is best way to get highest ethanol yield?28.25 g/L?that using C.utilis fermenting firstly,and then removing the most of C.utilis by centrifugation,adding P.stipites at last4.The process optimization of C.utilis and P.stipites stepwise fermenting the P.sajor-caju 25 days pretreated corn stover hydrolysis was studied.The results indicated that the liquid loading,C.utilis fermentation time,P.stipites fermentation time and temperature were the significant factors affecting ethanol yield.The optimized condition was the liquid loading in29.59 mL,C.utilis fermentation time at 32.47 h,P.stipites fermentation time at 51.77 h and temperature at 23.41?,and it could obtain the 32.24 g/L of ethanol yield.This subject has guiding significance for the production of ethanol by corn stover fermentation.