Co-fermentation Of Blue Algae With Straw And The Characteristics Of Microbial Communities During Bio-gas Production

As a major agricultural province, Anhui has a huge production of straws annually. Straw as a secondary product in the agricultural production is a kind of biological energy which can be easily obtained. In recent years, due to serious eutrophication, Chaohu, as one of five largest freshwater lakes in China, has been faced with environmental problems caused by blue-green algae outbreak. Blue-green algae, which are rich in organic matters, are recognized as biomass resources. Through the process of anaerobic fermentation, straws and blue-green algae can be converted into clean energy, this process can protect environment and maximize utilization of resources. The process of bio-gas fermentation requires the participation of microorganisms in different stages, thus the analysis on microbial community’s structure and function has become a hot research area. With its applications into the identification of microorganisms, molecular biology techniques are used to study microbiological changes in the process.In this paper, bio-gas fermentation experiments are conducted in self-made devices for the anaerobic reaction mixed with straws and blue-green algae. There are two devices, experimental group is pretreatment straws by 6% NaOH, and control group is un-pretreatment. The result shows that the bio-gas production of experimental group is slightly better than that of control group. The result shows that the bio-gas production of straws pretreatment by 6% NaOH is slightly better than that of control group. The fermentation device with pretreatment straws inside starts working quickly, and the maximum daily bio-gas output of 600 mL can be realized in the second day, while that of control group is 406 mL. The methanol content can be as high as 65% in pretreatment group, higher than 55% in the control group.The bio-gas fermentation is completed through the interaction between abundant microorganisms, including a series of bacteria and archaeon which can make methane, and the replacement of microbial communities correspondingly occurs in different methane producing stages. The description of microbial communities in bio-gas fermentation process can provide the theoretical foundation for the regulation of bio-gas fermentation. In this paper,16S rRNA gene clone library technique is used for the researches on the diversity of a series of bacteria and archaeon in the un-pretreatment straws device in different methane producing stages. The samples of anaerobic fermentation fluid has been collected severally in the early stage, the peak stage, and the termination stage of gas yield, and 16S rRNA gene clone library technique are used to delve into the diversity of bacteria and archaeon in these three stages. Two major conclusions have been achieved as a result:Firstly, the anaerobic fermentation system mixed with straws and blue-green algae includes 6 phylum’s bacteria:Firmicutes, Proteobacteria, Bacteroidetes, Chloroflexi, Spirochaetes and Ignavibacteriae. Predominant bacteria differ in different fermentation processes:In the early stage, OTU, with the largest abundance in bacteria communities, belongs to Proteobacteria, accounting for 30.6% of the total; In the peak stage, OTU, with the largest abundance in bacteria communities, belongs to Bacteroidetes, accounting for 27.6% of the total; In the termination stage, OTU, with the largest abundance in bacteria communities, belongs to Proteobacteria, accounting for 24.4% of the total.Secondly, in the anaerobic fermentation system mixed with straws and blue-green algae, archaeon belong to Euryarchaeota and are classified as Methanomicrobia, Methanobacteria and Thermoplasmata. In terms of genus, they can be further divided into Methanoregula, Methanobacterium, Methanosphaerula, Methanosarcina, Methanosaeta, Methanolinea, Methanomassiliicoccus, Methanospirillum and Methanobacteria, in which Methanoregula and Methanosarcina predominate. Different archaeon show different trends in the process of fermentation: Methanomicrobia decrease after their initial increase, Methanobacteria reduce and vanish rapidly from the outset, while Thermoplasmata emerge only in the termination stage.