Simultraneous Saccharification And Co-fermentation For Production Of High Titer Cellulosic Ethanol From Lignocellulose By Dry Milling Biorefinery Processing

Dry milling biorefinery processing(DMBP)were applied into cellulosic ethanol production for the purpose of maximizing the biorefining efficiency of lignocellulose by minimizing energy consumption,fresh water input,and waste water generation.The biomass solids loading of the typical lignocellulose feedstocks is maximized at each step of the biorefining processes.The DMBP starts with the "dry" dilute acid pretreatment(DDAP)with the initial solids of 70%(w/w)and the pretreated solids of 50%(w/w)with minimum water(steam)input and zero wastewater generation.The pretreated lignocellulose is fed to the "dry"biodetoxification for the fast and complete removal of inhibitors with no water input and output.The "dry" pretreated and biodetoxified lignocellulose is consequently fed to the "dry"hydrolysis and fermentation by simultaneous saccharification and co-fermentation(SSCF)with very high solids content(up to 25-35%).In addition,in order to improve the competitiveness of cellulosic ethanol for corn ethanol,must improve the titer and yield of cellulosic ethanol,and choose high performance,low cost industrial cellulase enzyme.The first part of this thesis is selected five different lignocellulose feedstocks,including the agricultural waste type of corn stover,wheat straw,rice straw,sugar industry waste type of sugarcane bagasse,forestry waste of Italian poplar wood chip were carried out to produce cellulosic ethanol by DMBP.At the optimal pretreatment and biodetoxification conditions,use Saccharomyces cerevisiae DQ1,at the moderate cellulase dosage(15 FPU/g Dry Matter)and high solids loading(30%,w/w),the final ethanol titer was 56.8 g/L,58.5 g/L,65.4 g/L,64.5 g/L,54.7 g/L,for corn stover,rice straw,wheat straw,sugarcane bagasse,poplar wood chip,respectively.These five feedstocks all well met the high fermentation titer required for industrial applications although with observable differences,which provides a wider range of raw materials and geographical scope for commercial production of cellulosic ethanol.The second part of this thesis is use five lignocellulose feedstocks to produce cellulosic ethanol by simultaneous saccharification and co-fermentation,pretreated material contains a large amount of xylose,Saccharomyces cerevisiae XH7 is a xylose utilizing yeast strain.Finally,by optimizing the fermentation conditions,the record high cellulosic ethanol performance was obtained:wheat straw feedstock achieved the maximum ethanol titer of 101.1 g/L or 12.8%(v/v)with the ethanol yield of 74.8%and the xylose conversion of 73.9%at the moderate cellulase dosage(15 mg proteins/g cellulose)and high solids loading(35%,w/w);corn stover achieved the most economically beneficial ethanol titer of 85.1 g/L or 10.8%(v/v)with the overall conversion ratio of 84.7%and xylose conversion of 87.7%at the low cellulase dosage(10 mg protein/g cellulose)and high solids loading(30%,w/w).The third part of this thesis is three major cellulase enzyme products available on the Chinese industrial enzyme market were selected and evaluated as the biocatalysts for the biorefining process of lignocellulose biomass into high titer ethanol.The cellulase enzymes included Cellic CTec 2.0 from Novozymes(Beijing),and LLC 4 from Vland(Qingdao),and#7(purchased from an industrial enzyme maker).The detailed assay on the filter paper activity,the cellobiase activity,and the total protein content of the enzymes were conducted according to the standard protocols.When the cellulase enzymes were applied to the practical hydrolysis and ethanol fermentation operation under the conditions of high solids and low range of cellulase dosage,the hydrolysis yield shows the significant difference and the difference was narrowed in the final ethanol yield.The commercially available cellulase enzymes showed the different performance in the activities,the cellulose hydrolysis yield,and the ethanol fermentation yield based on the protein dosage per gram of cellulose of corn stover.In general,the industrial cellulase products are satisfactory to be applied into the practical cellulosic ethanol production in commercial scale.Conclusively,these five feedstocks all well met the high fermentation titer required for industrial applications although with observable differences,In addition,the high cellulosic ethanol performance was obtained by simultaneous saccharification and co-fermentation,the three industrial cellulase products are satisfactory to be applied into the practical cellulosic ethanol production in commercial scale.These results could provide a strong theoretical basis for the industrial development of cellulosic ethanol production by dry biorefining technologies.