Screening Of Trichoderma Spp. And Its Biodegradation Mechanism Of Shanxi Lignite

Microbial liquefaction technology is a new field of research on clean utilization of coal resources.Different microorganisms have different solubilization ability for coal,and there is extensive research in the field of fungal degradation of low-rank coal,and coal bioconversion technology is one of the important ways to convert low-rank coal with low utilization rate into alternative fuels and non-fuel organic chemicals.In this paper,a fungal strain A-1 was isolated from the seeds of white Tremella and identified as Trichoderma citrinoviride by sequencing the 26S r DNA D1/D2region,and the fungus was used to study the degradation of Shanxi lignite,discuss the enzyme-producing characteristics of the fungus,and analyze the degradation products using modern analytical instruments such as elemental analyzer,X-ray diffractometer,scanning electron microscope,gas chromatography and mass spectrometer,and Fourier infrared spectrometer to investigate the intrinsic liquefaction mechanism of the strain on coal,and the main conclusions obtained are as follows.(1)In this study,three strains were screened from the seeds of white Tremella,and through the pre-experiment of degradation of the strains,it was observed that among the three strains,only strain A-1 could grow using coal,indicating that the strain A-1 might have the ability to degrade Shanxi lignite;through the analysis by molecular biology identification,it was determined that strain A-1 belonged to Trichoderma spp;in this paper,the microbial strain of strain A-1 was preserved using the conventional transfer slant cryopreservation method,which is the first time to use the strain in the seeds of white Tremella to degrade Shanxi lignite.(2)To facilitate the quantitative evaluation of the degradation ability of this fungus,this study used liquid medium coal solubilization method to conduct degradation experiments using this fungus A-1,and it was concluded that the degradation rate of this fungus reached 35%for H₂O₂pretreated Shanxi lignite in 20 d at a temperature of 25°C and a speed of 150 rpm.(3)By studying the elemental composition and structure of the coal,the changes of the coal before and after degradation were analyzed.The industrial analysis concluded that the moisture content in Shanxi lignite is high,which is not easy to burn,and the volatile matter is as high as 41.37%,which can increase the biological sensitivity of this coal sample and is more favorable to microbial degradation.The elemental analysis shows that the carbon content in the original sample of Shanxi lignite is 71.69%,which is a low-rank coal,and the C and H contents of the original coal are obviously reduced after H₂O₂pretreatment,from 71.69%and 15.69%respectively to 69.74%and 10.14%,and the O content in this Shanxi lignite was high,and the oxygen content increased from 4.48%to 12.07%after pretreatment;as shown by scanning electron micrographs,the morphological structures of the original coal and the hydrogen peroxide-treated oxidized coal did not differ much,both of them were lamellar structures with rough surfaces,which reflected the plant fibrous structure of lignite to some extent.The morphology of the residual coal after microbial action,with obvious changes,a large number of pores appeared and the pores increased,indicating that the microorganisms changed the macromolecular structure of the coal particles;the mineral content of the raw coal was higher than that of the oxidized coal as shown by X-ray diffraction analysis,and the related characteristic peaks of Ca CO₃disappeared in the coal samples oxidized by H₂O₂,probably due to the change of Ca CO₃by the pretreatment of hydrogen peroxide,indicating that the pretreatment process of the coal samples reduced the inorganic mineral mass and relaxed the intermolecular forces of the coal macromolecules,thus improving the microbial degradation of the coal.(4)The UV-Vis spectra of the liquid phase products after degradation showed that the absorption intensity was weak at the early stage of degradation(1d,4d)and gradually increased with the increase of degradation time,in which the A290 value of liquefied products showed a trend of increasing and then gradually stabilizing with the increase of degradation time.The analysis showed that the absorbance of the side chains of aromatic rings was larger in the degraded residual coal samples compared with the lignite samples pretreated with H₂O₂,indicating that complex structures such as aromatic rings were opened during the biodegradation of lignite and a variety of side chains were generated,and the degraded residual coal residues contained more oxygen-containing functional groups,which might be caused by the degradation of specific functional groups by the bacteria,and the degradation products contained some amines and esters The degradation products were analyzed by gas chromatography-mass spectrometry(GC-MS)using dichloromethane,ethyl acetate and n-hexane,respectively,and the results showed that the degradation products mainly contained organic substances including alkanes,alcohols,esters and other aliphatic compounds and phenolic organic substances.(5)The 20-d dynamic detection of extracellular proteins secreted by fungus A-1showed that the content of extracellular proteins gradually increased with the increase of liquefaction time,indicating that the fungus produced a large amount of extracellular proteins.The changes in the concentration of extracellular protein produced by the fungus were mainly based on the changes in extracellular enzymes,indicating that the A-1 fungus secreted a large amount of extracellular enzymes.The crude enzyme solution was analyzed for oxidase,laccase(Lac),lignin peroxidase(Li P)and manganese peroxidase(Mn P)activities,and the activities of lignin peroxidase and oxidase were detected to be much higher than those of laccase and manganese peroxidase,with Li P activity reaching its highest on day 12 with an enzyme activity of 90 U,while oxidase activity reached its highest on day 9 with an enzyme activity of 42 U On day 14,these four enzymes did not reach the highest activity and there was a lag in enzyme activity,which may be due to the fact that the degradation of lignite is not the effect of extracellular enzymes alone,but the result of compounding multiple extracellular enzymes.