Screening And Dominant Population Analysis Of Microbial Strains In Biogas Fermentation Under The Low Temperature

Biogas is one of clean energy. In recent years, under the policy encouragement and thefinancial support, the rural household biogas in China has been developed rapidly.However, there are still deficiencies existed in the controlling process of biogasfermentation, which include in terms of long starting time, low utilization rate of rawmaterials, improper process control, etc. The poor quality of biogas produced under lowtemperature is the main factor of restricting the development of biogas.The biogas fermentation is a complex anaerobic digestion process, as it involvesmaterial decomposition and the production of multi-microorganisms such as acid,hydrogen, methane, etc. Therefore, the key of developing and utilizing excellentresources of microorganism as well as supervising the production of biogas is toprecisely study the composition of flora under an excellent biogas fermentation systemand discover predominant flora. This research aims to use biogas slurry collected fromdifferent areas as inoculating sources, selecting excellent inoculating sources under lowtemperature through the stimulated fermentation test with staged cooling. Differentfermentation strains under low temperature such as ZG2, CW1, HL2and theircorresponding inoculating sources ZGB, CWA, HLB are used as testing materials. Thestudy makes an analysis of the composing diversity of micro flora in biogas slurrythrough the PCR-DGGE technology, gene cloning and gene sequencing, the results are asfollows:1. Collecting12samples of biogas slurry which can produce qualified biogas underlow temperature from areas of Guyuan County in Zhangjiakou, Pingquan County inChengde and Linzhang County in Handan. The12samples are as follow: HLA, HLB,HLC, ZGA, ZGB, ZGC, CPA, CPB, CPC, CWA, CWB and CWC. Take these12samplesas inoculating sources, carrying out a40days biogas fermentation test under differenttemperature conditions of16°C,13°C,10°C and5°C respectively. Judging from thecomparison of three index in terms of total gas production, gas production rate and themethane content, we can draw the conclusion that the No.5dealing group which theinoculating source is the biogas slurry sample—ZGB, collected from Guyuan County inZhangjiakou, produced the optimal fermentation biogas under low temperature. The totaloutcome of biogas in NO.5dealing group is15,910.4cm3,under the temperature of10°C, its gas production rate reaches0.048m3/(m3·d) and the methane content is63%.2. The microbial diversity of testing samples is abundant. However, due to differencesin terms of inoculating sources, raw materials and temperature, microbial composition inthe sample is largely disparate. The similarity coefficient of microorganisms in thesample also indicates that different fermentation conditions and environment will lead tochanges of the diversity of microbial composition in the process of fermentation.3. The analyzing results of gene cloning and gene sequencing show that maindominant strains in the sample are Methanosarcina, Methanosaeta andMethanocorpusculum.4. The7thstrip of the inoculating source (ZGB) in the DGGE map as well as thefermentation strain (ZG2) in the sample is Methanosarcina. This is the only strip whichoccurs in the same place in the sample ZGB and the sample ZG2, and there are no otheradvantaged strips which occur in the horizontal position. In conclusion, Methanosarcinais the key flora which maintains normal biogas production under low temperatureenvironment.