Construction Of Composite Microbial System On Efficient Methanogens And Applied Research

Methane fermentation is a complex biochemical reaction process which unites by avariety of microorganisms, in the fermentation, growth of methanogens andnon--produce-methane microorganisms make a dynamic equilibrium. Methanogen is the keymicroorganism in methane fermentation, which plays a critical role in the output and qualityof the biogas. At present, natural vaccination is mainly utilized in methane production, as aresult, there are such problems including low gas-produce rate, the instability of gasproduction and low digester utilization under cold weather conditions. Therefore, it issignificant to do the research，such as screening methanogen with excellent traits for biogasproduction, studying their physiological and biochemical property and taxonomic status,determining the influence of various factors on the growth, constructing efficient biogascomposite microbial strains in virtue of natural and artificial methods, and finally applying tobiogas production. The research can not only enrich species resources of the methanogenicarchaea, but composite strains built can enhance the activity of the microbial community inthe various stages of methane fermentation, and possess great practical value on efficiencyand stability of methane gas production.By Hungate anaerobic technique,three strains(designated SHB,AG and QDW) wereisolated from the diverse anaerobic environments such as wetland sludge, sewage treatmentplant and so on.The analysis of morphological, physiological and biochemical characteristicsand16S rDNA sequences determine taxonomic status and growth characteristics.The strainSHB and AG ascrib to Methanobacterium sp..The strain SHB can use H2/CO2and sodium assubstrate and grow fastest in the Na+concentration range of0-5%,and the optimum range ofgrowth temperature and pH of strain SHB is16-40oC and6.0-9.0.The strain AG can alsoutilize H2/CO2and sodium as substrate,the optimal temperature is37o C, and the optimal pHis7.5-8.0, Na+concentration is less than1%.The strain QDW is a member of Methanoculleusgenus,which can grow vigorously at37oC and at pH7-7.5with H2/CO2,sodium andsodium acetate as substrate. Compared with the strain AG and QDW,the strain SHB shows optimal ability at a wide range of temperature and pH, and has the stronger salt tolerance andhigher growth rate, the composite system will be constructed by adding in the strain.Relying on one or a few culture is difficult to regulate the overall methane fermentation.Therefore, at different temperature,each sample is enriched and domesticated, finally mixed.Medium-temperature composite system C13, C14, and B3, and low-temperature compositesystem C2-1and C2-3were constructed by a few of the better composite system and strainSHB mixed culture. In three medium-temperature composite system,the methane productionability of composite system C13, of C14and B3was increased by4.44%,1.19%and9.41%,composite system C13and B3was significantly higher than the control, while theimprovement of composite system C14is not significantly; Compared with composite systemB2-1and the strain SHB, methane-producing capacity of low-temperature composite systemC2-1was enhanced by5.74%and4.82%, while composite system C2-3was improved by20.48%and5.62%in contrast to composite system B2-3and the strain SHB,respectively.The composite system C2-1and C2-3was significantly higher than the control.The medium-temperature and the low-temperature composite system were used forsmall-scale biogas fermentation experiment, respectively. At35oC, the processing groupadded in composite system C13increase methane yields by37.41%,which is significantlyhigher than the groups that have composite system C14and B3,respectively.At16oC,thegroup is a32.84%increase in biogas production compared with control by adding compositemicrobial system C2-3, a biogas increase by addition of composite system C2-3issignificantly higher more than C2-1addition.