Study On Fermentation Of Cellulosic Ethanol By Escherichia Coli Using Brittle Rice Straw

Cellulosic ethanol, as a biomass energy that can substitute for petroleum resources,has received the widespread attentions. Brittle rice straw, a new kind of biomassresource, was used as the research object to ferment and produce ethanol, trying to finda new straw utilization way. The components of the brittle straw were analyzed andcompared with that of control, a normal straw. Then it was compared that thecomponent difference of total reduced sugars and main products released from the twokinds of straws by acid or alkali pretreatment. Further more the effects of theby-products from straw pretreatment on ethanol fermentation by Escherichia coli werestudied. Finally the conditions and process of ethanol fermentation on brittle straw wereoptimized.Composition analysis of brittle straw(Coded2006C28，Breeding from Yangdao6，Oryza sative.L)were performed by comparison with the control, normal straw. Cellulosecontent of brittle straw was lower than the control by15%, hemicellulose and lignincontent was higher than that of the control by17%and5%respectively. With2.0%H2SO4(w/v) to pretreat on the materials, sugars released from the brittle straw was13%higher than that of the control. The glucose and xylose yields obtained from the brittleone were1.38and1.06times higher than that of the normal straw respectively. Butthere was no significant difference between the arabinose yields produced by the twostraws. And by-product (except formic acid) such as acetic acid, furfural and5-HMFhad no prominent difference from the two rice straws. Enzymatic saccharification werefurther carried by adding cellulase to the dilute acid hydrolysate of the straws with theoptimum conditions, the total produced sugars of541.2±8.0mg per gram dry strawwere produced by the brittle straw,41.9mg higher than that of the control. Meanwhilethe contents of glucose and xylose generated from the brittle straw were higher by12%and24%than that of control, respectively. And the arabinose yields obtained from thetwo materials had no obvious difference. The result of observation on the materialsurface morphology by scanning electron microscope indicated that the brittle strawcells were more vulnerable to damageThe effects of by-products from pretreatment on ethanol fermentation byEscherichia coli SZ470was further explored, the results showed that the concentrationof acetic acid exceeded1.2g/L would restrain the cell growth of SZ470by100%. Thecell growth was also100%inhibited while the concentration of catechol reached up to3.0g/L. Moreover，the content of furfural at1.2g/L was the most toxic to the cell growth.The response surface analysis indicated that the synergy effect of acetic and furfuralcombination on the cell growth and ethanol yield of SZ470was significant and itshowed a proactive role. However when furfural and catechol was combined, there wasa significant coordinate repression on ethanol yield.Finally, the optimum conditions of ethanol fermentation by using straw hydrolysate were inoculum size at5%,35℃and initial pH at6.5. The concentration of ethanolfrom brittle straw with separate hydrolysis and fermentation was12.94±0.60g/L，which was higher by29%than that of the control(10.06±0.59g/L). In the case ofsimultaneous saccharification and fermentation by E.coli strain for96h, the ethanolconcentration from the brittle straw was1.25times higher than that of the normal straw.