The Study On Degumming Bacteria Screening And Effect Of Its Pretreatment On Sugar Production By Enzymatic Hydrolysis Of Eichhornia Crassipes Biomass

Eichhornia crassipes is rich in cellulose and hemicellulose,it can also be used for the second generation bioethanol production.Pretreatment is believed as an indispensable step for bioethanol production,and biological pretreatment has been paid more and more attention because of its low energy consumption,low pollution and environmental friendliness.Biological degumming is the necessary step of ramie fiber textile utilization,after degumming process,ramie can effectively remove the non-cellulosic components and retain relatively complete plant fiber.In this paper,isolation medium in which pectin was the sole carbon source was used to screen degumming bacteria from the environment where Eichhornia crassipes grew.The strains obtained by Congo red staining plate were directly applied on the pretreatment of fresh sample of Eichhornia crassipes,and then the best Eichhornia crassipes degumming strains were got through the comparison on ratio of sugar yield and sugar consumption.Orthogonal experiment was used to optimize the pretreatment conditions.After comparing sugar production efficiency increment of enzymatic hydrolysis of Eichhornia crassipes substrate pretreated by degumming bacteria(CTS-BQ1),phanerochaete chrysosporium and pectinase under their optimal pretreatment conditions,the difference of sugar production efficiency and pretreatment mechanism were analysized and the best biological pretreatment was obtained.On this basis,biological pretreatment was combined with chemical pretreatment to reduce the consumption of chemical reagents and further improve the efficiency in enzymatic hydrolysis of Eichhornia crassipes.Microbial degumming was used as pretreatment method to improve sugar production efficiency of enzymatic hydrolysis of Eichhornia crassipes for the first time,in order to provide a new source of strain for biological pretreatment.The main results are as follows.(1)This research selected 12 strains of Eichhornia crassipes deguming bacterium which grew from Eichhornia crassipes growth environment and obtained 8 strains of degumming bacteria that have higher hydrolysis circle diameter and colony diameter(H/C),in which CTS-BQ1 produced sugar the most and consumed sugar the least.Compared with raw materials,the sugar efficiency of Eichhornia crassipes substrate pretreated by CTS-BQ1 improved 37.4%.CTS-BQ1 was identified as Bacillus axarquiensis with 16S rRNA technique.(2)Pectinase is the main enzyme secreted during the pretreatment process of Eichhornia crassipes with CTS-BQ1.The influence sequence of different factors on the activity of pectinase secreted by CTS-BQ1 is temperature>treatment time>inoculums size>initial pH.The influence sequence of different factors on degumming bacteria concentration is treatment time>initial pH>temperature>inoculums size.The influence sequence of different factors on enzymatic hydrolysis sugar yield of Eichhornia crassipes substrate pretreated by CTS-BQ1 is initial pH>temperature>inoculums size>treatment time.The optimized pretreatment condition for CTS-BQ1 pretreatment conditions are,the pretreatment temperature 35℃,the initial pH 9,the inoculums size 2%and the pretreatment duration 3 days.Under the optimal conditions,degumming bacterial pretreatment achieves 142 milligrams reducing sugar per gram Eichhornia crassipes.(3)During the process of degumming bacterial pretreating Eichhornia crassipes,deguming bacterial mainly removed ethanol extracts that including gum,which can effectively increase the degree of nudity without consuming cellulose.Degumming bacterial achieved 142 milligrams reducing sugar per gram feedstock after 3 days of pretreatment,and produces 13.81 milligrams more reducing sugar per gram feedstock than control group.During the pretreating process of Eichhornia crassipes by Phanerochaete crysosporiurn,granular objects of the lignin oxidation attached to the surface of the substrate,so as to achieve lignin removal,but it also took part of cellulose away when lignin was removed,and that significantly reduces the water retention value of the substrate.Phanerochaete crysosporium pretreating fresh Eichhornia crassipes achieved 87.68 milligrams reducing sugar per gram feedstock after 10 days of pretreatment,and produced 8.78 milligrams more reducing sugar per gram feedstock than control group.During the process of pectinase pretreating Eichhornia crassipes,pectinase mainly removed ethanol extracts that including gum.The effect of pectinase on the surface of the substrate was covered because of substrate destruction caused by acid under high temperature and high pressure.Pectinase pretreatment achieved 162.92 milligrams reducing sugar per gram feedstock after 3 days of pretreatment,and produces 11.92 milligrams more reducing sugar per gram feedstock than control group.Three kinds of biological pretreatment achieve 3.0 times,1.8 times and 3.5 times more reducing sugar yield than untreated Eichhornia crassipes,respectively.With consideration of reducing sugar yield,pretreatment duration and pretreatment cost,degumming bacterial pretreatment was selected as optimal biological pretreatment method.(4)Compared with reducing sugar yield of Eichhornia crassipes substrate pretreated by combined pretreatment of degumming bacterial and dilute acid(1%w/v H2SO4),reducing sugar yield of Eichhornia crassipes substrate pretreated by combined pretreatment of degumming bacterial and dilute alkaline(1%w/v NaOH)had a significantly improvement.Under the mild condition of alkali pretreatment,the yield of reducing sugar was promoted by degumming bacteria in combined pretreatment with dilute alkali.Compared with the control,the maximum yield of reducing sugar increment was 25.72 milligrams more reducing sugar per gram feedstock,which was about 1.86 times higher than that of individual biological pretreatment.When the intensity of dilute alkali pretreatment increased,the biological pretreatment could inhibit the yield of reducing sugar.