| Lignocellulose biomass is one of the most abundant resources in the world which owns the advantages of cheap and renewability.Lignocellulose is composed of cellulose,hemicellulose,and lignin,in which cellulose and hemicellulose can be hydrolyzed into soluble sugar,and then fermented for biofuel production.However,the high cost,low efficiency,and low compatibility of lignocellulose hydrolysate with the following fermentation process has greatly hindered its application on biofuel industry.Thus,seeking a high efficient,cost effective,and environmentally friendly cellulose hydrolysis method is crucial to realize the resource utilization of lignocellulose.This study aimed to achieve high-yield hydrogen production from lignocellulose saccharification products.Through the screening of lignocellulose-degrading bacteria,obtained the dominant strain with high efficiency of lignocellulose saccharification.Meanwhile,the mechanism of bacterial saccharification cellulose was analyzed from the perspective of enzymology.Established a pretreatment method for lignocellulose that enhances the saccharification of lignocellulose.Promotion the saccharification efficiency by optimizing the pretreatment parameters.To construct a bio-hydrogen production system for lignocellulose-saccharification,analyzed the influence mechanism of lignocellulosic saccharification and the key factors of hydrogen production by combined lignocellulose saccharification bacteria with hydrogen-producing bacteria.Provided a theoretical basis for the utilization of agricultural waste and the feasibility of biotransformation.In this study,a cellulosic bacteria Rominiclostridium thermocellum M3 with high cellulose saccharification capacity was isolated from horse dung.strain M3 not only able to saccharified Avicle,but also saccharified natural lignocellulosic materials such as rice straw,corn stover,corn cob,and poplar sawdust.When the 5 g/L Avicel used as substrate,the soluble sugar yield up to 481.5 mg/g Avicel after 72 h under 60 oC,p H 7.5.what's more,about 97% glucose content in the Avicel hydrolysis.In order to evaluate the ability of strain M3 saccharified lignocellulose,the natural lignocellulose biomass were hydrolyzed by commercial cellulase.It was found that when the substrates were not pretreated,the strain M3 saccharification efficiency reached 80% of the commercial cellulase.The analysis of cellulase activity and metabolites of strain M3 revealed the mechanism of bacteria saccharification lignocellulose.The result shows that the organic acids produced by strain M3 inhibited its own metabolism and reduced the consumption of soluble sugars,meanwhile,the cellulase continue to hydrolyze the cellulosic substrate at this point,which is the mechanism of the strain M3 saccharified cellulose.The removal of lignin in lignocellulose is of great significance for improving the utilization of such raw materials.Based on the superiority of Fenton reagent in the pretreatment of lignocellulose,this study simulated the biological process of fungal degradation of lignin and established a pretreatment method of chelating Fenton reagents.This study found that citric acid can maintained the oxidization of chelating Fenton reagent under near-neutral conditions,remove lignin while maintaining cellulose hemicellulose,and enhance the saccharification effect of strain M3.By optimizing the pretreatment conditions,the lignin degradation ratio in rice straw was measured under conditions of 0.03 mol/L Fe Cl3,2.25 mol/L H2O2,0.03 mol/L citric acid,p H 6.0 for 24 h.More than 50% lignin was removed and the total cellulose recovery is close to 85%.The SEM,FTIR,XRD and analytical methods were used to comprehensively and systematically analyze the structural characteristics of straw pretreated by chelating Fenton reagents.It was clarified that by removing lignin,reducing the crystallinity of the substrate,and destroying the substrate structure enhanced the lignocellulose saccharification by bacteria.The saccharification results showed that pretreatment with chelating Fenton reagent increased the saccharification ratio by 169%.Through the coupling of lignocellulose saccharification bacteria and hydrogen-producing bacteria,constructed the integrated system of lignocellulose saccharification-fermentation-hydrogen production,which enhanced the utilization efficiency of cellulose/hemicellulose.Chelate-modified Fenton like reagent pretreated rice straw as the substrate and saccharified by strain M3,then fermented the lignocellulose hydrolyzate by the Thermoanaerobacterium thermosaccharolyticum W16,aim to investigate the effect of lignocellulose saccharification by bacteria on the biohydrogen production.The hydrogen production of SSF was 8.92 mmol/g and SHF was 1.52 mmol/g rice straw which was just 17% of the SSF.In contrast,the CBP hydrogen production was 5.74 mmol/g rice straw under optimum condition.To further evaluate the effect of bacterial saccharification on hydrogen production,a modified Gompertz model was used to fit the hydrogen production curve.The results showed that the maximum rate of hydrogen production by SSF was 0.26 mmol/L/h,which was much higher than CBP of 0.16 mmol/L/h and SHF of 0.07 mmol/L/h.In addition,the simultaneous hydrogenation of saccharification showed that the combination with strain W16 not only increased the tolerance of strain M3 to the acidic environment,but also increased the utilization of cellulose and hemicellulose by 28% and 69%,respectively.The result shows that the bacteria saccharification rice straw has good application prospects in lignocellulose biorefinery,meanwhile,established a good experimental basis for achieving efficient lignocellulosic biohydrogen production. |
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