| Bio-ethanol converted from low priced and abundant lignocellulosic materials isa potential renewable resource to replace depleting fossil fuels. Lignocellulosicmaterials are the largest origin of hexose and pentose. Xylose is the dominatingpentose in hemicellulose, only second to glucose in all monosaccharides natural oflignocellulosic hydrolysate. Regarding industrial kelp slag waste as raw material ofcontinuous ethanol fermentation. This research is to study and optimize the hydrolysiscraft and fermented craft utilizing recombinant Escherichia coli strain (KO11) whichcan transform various reducing sugars to bio-ethanol production.Kelp slag is the remnants after the alginate extracting, containing mounts ofcellulosic materials. As investigated in many papers, kelp are plants which are rich,available and easy to get from ocean, which can be taken to produce bio-energy.Figures of components in kelp slag shows that it is high in cellulose by25.88%,hemicellolose by12.52%and little in acid-insoluble lignin, which live up to the idealfeedstock of the ethanol fuel.It is essential to polish the pretreatment, via improving the hydrolysis efficiencyof cellulose by enlarging the reaction surface of kelp slag and enhancing the finalyield of glucose for the following fermentation. The fermentable sugars’ ingredientsfrom kelp slag was studied by dilute sulfuric acid pretreatment and further enzymatichydrolysis. Sulfuric acid pretreatment was conducted on the density of0.1,0.2,0.5,1.0,2.0and3.0%(w/v) for1.0h,121℃. The maximumenzymatic hydrolysis ratecan climb to93.32%under the optimal condition of dilute sulfuric acid pretreatment(2%sulfuric acid, substrate concentration12.5%,121℃,1.0h)and enzymatichydrolysis of cellulose (50℃, pH5.0,16h).E. coli KO11has been proven to metabolize all major sugars, which are the constituents of hemicellulosic hydrolysates in anaerobic conditions. The combinedutilization of xylose in hemicellulose and glucose in cellulose by KO11can offer anopportunity to reduce manufacturing cost of bio-ethanol. Through single factorexperiments and one way anova, the optimized conditions are:(1)20g/L sugarsfermentation (glucose and xylose, rexpectively): they share the same optimaltemperature and pH at37℃and5.5; while after the static culture following the rotaryshaking of4h and8h, the highest ethanol conversion rate can rise to94.81%and94.15%, respectively;(2) KO11has wonderful ethanol conversion performance at43℃;(3)Fucose, xylose, mannose, galactose, and glucose are applicable for KO11toproduce ethanol;(4)50g/L glucose is a favor for KO11;(5) Xylose do not work wellwhen the concentration of glucose is more than4g/L until the glucose is used up.Three fermentation processes——Step hydrolysis and co-fermentation (SHCF),Simultaneous saccharification and co-fermentation (SSCF), Nonisothermalsemisimultaneous saccharification and co-fermentation (NSSCF)——were discussedin this research. KO11was adopted to take advantage of hydrolyzed reducing sugars.Consequence indicated that monosaccharides released from pretreatment andenzymatic hydrolysis can be fully fermented into ethanol by KO11. Compared withSHCF and SSCF, NSSCF is the most acclaimed. After NSSCF（inoculated afterenzymatic hydrolysis for6h）50h, the ethanol conversion rate can reached87.67%theoretically, which shows brilliant prospect for kelp slag.As a general view, on the premise of dilute acid pretreatment, KO11can effectiveutilize the industrial kelp slag hydrolysis by NSSCF, which reveals considerableprospect for bio-ethanol production. This study concerns the traditional fermentation,further problems should be explored in the later work, such as the factors inpretreatment and fermentation. |
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