| As an excellent renewable liquid fuel,ethanol has attracted wide attention.Microalgae is a kind of biomass resources with high photosynthetic efficiency and high yield.Many kinds of the algae cells contain a large amount of starch,cellulose(I?)and other polysaccharides,which are the excellent raw materials for the preparation of fuel ethanol.The development of the technology that using microalgae for the preparation of fuel ethanol can alleviate the increasingly severe energy shortage in China,reduce greenhouse gas emissions and environmental pollution,thus,have excellent prospects for application.The high cost of preparing microalgae biofuels is the main limiting factor for the development of this technology.According to the presupposition technology,the production cost of microalgae fuel ethanol concentrates on the cultivation,harvesting and enzymatic hydrolysis of microalgae.Therefore,it is imperative for microalgae fuel ethanol industry to explore the low cost integrated process and reduce the production cost of microalgae.In view of the bottleneck problem of high density carbohydrate culture and the high cost of energy conversion,this study improves the conversion efficiency of biomass fuel through the selection of carbon rich microalgae with high environmental tolerance and the scale culture of outdoor photo bioreactor,and improves the conversion efficiency of biomass fuel,and the process of simultaneous fermentation of high concentration algal carbohydrate enzymes and so on.In the field of research,we focus on the deep mechanism of the inhibition effect of high concentration substrate enzyme solution,and analyze the key mechanism of improving the efficiency of enzymatic hydrolysis,and give a comprehensive and systematic assessment of the transformation process of energy microalgae,and provide a definite technical guidance for accelerating the industrialization process of microalgae fuel ethanol.For the above contents,the following works are carried out.1.Identified the fine carbon rich algae selected in the experiment,and evaluated the biomass yield and environmental tolerance in the outdoor large-scale internal column bioreactor,outdoor flat plate photo bioreactor and the runway pool bioreactor.After 15 days of culture,the dry weight of microalgae reached 2.157g/L.The biomass yield of microalgae could reach 28.77g/d m~2,the total carbohydrate content was 45.40%.And after 30 days cultured in the 200m~2 open runway pool,the cell density reached 1.092g/L,the carbohydrate content reached 38.10%,and the yield per unit area reached 12.72g/d.m~2.2.The effects of alkali pretreatment conditions on the depolymerization of cell wall fiber structure and the starch granule dissolution behavior of algal cells,as well as on the subsequent substrate enzyme hydrolysis rate,total sugar yield and conversion efficiency were analyzed.The proportion of dextran and total sugar in alkali treated algae residue reached 35.45%and 46.4%,respectively,and increased by 38%and 32.1%,respectively,compared with the control.The results of electron microscopy and infrared spectroscopy showed that alkali treatment mainly acted on the depolymerization of cell wall polysaccharide(cellulose,hemicellulose analogues),and promoted the change of the crystal structure of cell polysaccharides and the dissolving of fat and protein with the cytoplasm.The yield of enzymolysis for 72h was 96.3g/L after pretreatment,which was 69%higher than that of the control group.The conversion rate was 5%higher than that of the control group by5%.3.The inhibition kinetics of enzymatic hydrolysis of high concentration substrates was studied,and the mechanism of different substrate concentration,the inhibition of external products and the reaction of surfactant to enzymatic saccharification were investigated.At low substrate concentration,the increase of appropriate concentration of enzymes helps to increase the yield of saccharification.However,the high enzyme concentration may inhibit the process of enzymatic hydrolysis,but the inhibition of product is weak.At the high substrate concentration,it is indicated that the effect of only increasing the concentration of the enzyme on the yield of the product is weak in the process of substrate concentration,and the anionic surfactant Tween 80 is ineffective by weakening the enzyme and ineffective.The adsorption of substrates to reduce the use of enzymes can effectively promote the enzymatic hydrolysis of low concentration systems.In addition,it is easier to increase the yield of glucose by adding the surfactant enzyme solution system and prolonging the reaction time.Hydrolysis at high enzyme concentration can also be used to accelerate the enzymatic hydrolysis process and reduce the cost of high concentration enzymatic hydrolysis.4.The pretreatment process was optimized by response surface methodology,fed batch enzymolysis for substrate after alkali treatment was also consummated,and the conversion efficiency of different enzymatic hydrolysis processes was comparatively analyzed.Based on the above response surface analysis,the best condition of glucose yield was obtained and verified:0.25mol/L NaOH,60min,72?.The batch feeding enzyme hydrolysis with 10%(w/V)solid initial hydrolysis,and finally reached 34%(w/V)solid load,after enzymatic hydrolysis 120h,the maximum glucan concentration was 129.50 g/L,which is the highest concentration of microalgae saccharification using enzymatic hydrolysis ever reported.The proportion of polysaccharide in microalgae treated by alkali was increased by 60%,indicating that the high solid mass substrate after NaOH pretreatment and feeding batch process for high glucose concentration is an effective solution to the inhibition of high concentration enzyme digestion.5.Based on the initial substrate concentration of batch feeding,the ethanol tolerance and fermentation performance of high substrate concentration were evaluated.The optimum pH and reaction temperature of synchronous saccharification and fermentation process(SSF)were optimized,and the same feeding scheme was adopted to improve the concentration of SSF reaction substrate,and the yield of high concentration of ethanol was finally obtained.6.The production cost of microalgae biofuel ethanol is mainly concentrated in the process of culture,harvesting,microalgae pretreatment and enzymatic fermentation.This study aims at a specific microalgae biomass,and the economic evaluation and cost analysis of algae species,culture mode,nutrition mode,production mode,collection mode,pretreatment,enzyme hydrolysis,and fermentation technology. |
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