| Straw is a kind of renewable resource which contains a large number of biomass energy,and the anaerobic fermentation of straw is an effective way of energy conversion.However,cellulose is covered by uneasily degradable lignin of the straw material that requires pretreatment to improve the efficiency of biogas producing in anaerobic fermentation.Biological pretreatment technology,which has the advantages of mild reaction conditions,easy to operate,no secondary pollution,is the best method in the current pretreatment technologies.In order to improve the efficiency of biological pretreatment,it is critical to isolate a microbe which can degrade lignin effectively.In this study,strain 1285 capable of producing laccase and degrading lignin effectively was screened from soil humus,and its preliminary identification was carried out.For improving the efficiency of this strain in pretreatment process,the assays of biological pretreatment-effectiveness evaluation,optimization of culture condition and application of biological pretreatment for anaerobic fermentation were also conducted.The following conclusion can be drawn:(1)Through screening and re-screening,a laccase-producing strain 1285 was isolated from soil humus.It could turn PDA-guaiacol media to fuchsia.The results of re-screening by submerged fermentation showed that laccase activity produced by 1285 was 395.06±3.67 U/L and higher than others,but lignin peroxidase,and manganese peroxidase enzyme activities were not detected.To evaluate biological pretreatment effectiveness of 1285,it was compared with Streptomyces rochei,and Pleurotus ostreatus which were existing pretreatment strains,the results revealed that the pretreatment-effectiveness of 1285 against wheat straw was high than others,especially the lignin degradation of non-sterile wheat straw was most apparent,so pretreatment of 1285 to non-sterile wheat straw showed the best performance in:the loss rate of dry matter,cellulose,hemicellulose,lignin being8.75±0.10%,2.54±0.20%,15.86±0.36%,16.92±0.63%,respectively.And the leaching solution SCOD,TVFA and reducing sugars of bio-pretreated non-sterile wheat straw by 1285 was 2180±20 mg/L,237.41 ±6.01 ?g/L and 241.63±7.95?g/mL.Thus 1285 showed the potential of application in biological pretreatment for straw material.On the PDA media,hypha of 1285 was white and villiform,it grew fast and could produce green spores.Under the microscope,the symmetric growth and conidium peduncles like tree branches were observed,its ITS gene sequenceshad99%similarity withthe corresponding sequence of Trichoderma asperellum(KM246751)in NCBI.On the basis of these characteristics,strainl285 was identified as Trichoderma asperellum1285.(2)In order to achieve batter results of biological pretreatment for straw material,single factor experiment and response surface methodology were used to optimize the culture conditions for T.asperellum 1285.By single factor experiment,optimum carbon was glucose at 30-70 g/L;optimum nitrogen was yeast extract at5-25g/L;optimum culture temperature was 25-35 ?;optimum pH was 2-4.By response surface methodology,the optimized conditions were as follows:glucose 49.73 g/L,yeast extract 13.93 g/L,pH 3.2,culture temperature 32?.Under these conditions,the dry weight of mycelium predictive value was 0.66g,and the actual value was 0.67±0.01 g,which was increased by 2.39 fold than the beginning.(3)To determine the optimal pretreat time of T.asperellum 1285 and study the biogas productivity of bio-pretreated wheat straw in anaerobic fermentation,the wheat straw was pretreated by T.asperellum 1285 for 0 d,2 d,4 d,6 d,8 d,10d,respectively.The results showed that biological pretreatment of wheat straw for 8 days achieved the best results.The loss rates of wheat straw were as follows:dry matter 6.13±0.32%,lignin 14.13±0.73%,hemicellulose 18.58±0.73%,cellulose 9.94±0.53%.The exposure of hemicelluloses observed by SEM further proved that lignin was effectively degraded after biological pretreatment,which is beneficial to improve anaerobic digestion efficiency.The anaerobic fermentation of wheat straw was held after wheat straw was bio-pretreated for 8 d,and total gas production was 14774.3±216.56 mL as well as methane production was 7638.9±165.36 mL for 50 d,with14.05%and16.01%higher than control respectively.But biological pretreatment had no impact on methane level.The above research results showed that T.asperellum 1285 was a useful microorganism to degrade straw and possessed of better application prospect in straw pretreatment process. |
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