Microbial Community Structure Of Anaerobic Digestion Sludge In Different Seasons:Insight Into Characteristic And Metagenomics

Background: It will be the development direction of organic matter treatment and disposal to realize efficient recovery of energy and material in the future.Anaerobic digestion is a promising technology for reducing organic waste and producing clean and reusable end products.Anaerobic digestion sludge(ADS)is an important source of related microorganisms,which has been used as inoculated in the digestion reactor.Its physicochemical characteristics and microbial community composition is of great significance to the stable operation of the digestion reaction.Despite the rapid development of AD,the full extent of microbial population structure in the system is not yet fully understood,which limits its widespread use in bio-energy production.Objectives: This study intends to collect ADS in different seasons to analyze the physical and chemical characteristics of sludge in different seasons,the composition and distribution of bacterial and archaeal communities and methanogenic metabolism,and to clarify whether there is an obvious advantage suitable for inoculation,in order to provide support for the subsequent use of microorganisms or optimization of microbial communities to promote the development of AD.Methods: The ADS in different seasons was sampled from an AD tank with stable operation and constant substrate type.Physicochemical analyses(pH,TS,VS,moisture,ash,and elemental composition)were performed.The microbial community diversity and composition were also compared.16 S r DNA amplicon sequencing technology was used to analyze the α-diversity(OTU number,Chao1 index,Shannon index),and to compare the composition and dominant bacteria and archaea.The roles and functions of main microorganisms,the effect of inoculating suitable sludge,and the results and benefits of AD were discussed or evaluated.Results: ADS from autumn and winter had a more suitable VS(3.68%;3.18%)and C/N(19.93;19.84),other physicochemical indexes were similar,and pH was close to the ideal range.Their α-diversity was higher in autumn and winter: OTUs,Chao1 and Shannon index of microbes were higher than those in spring and summer.Although the relative abundance of the stable dominant microbiome was different in different seasons of sludge,the bacteria and archaea groups were similar,especially in the level of large taxonomic phylum and order.Firmicutes and Bacteroidetes accounted for more than 60% of the bacterial community,Proteobacteria and Synergistetes followed;while archaea belonging to Methanobacteriales,Methanomicrobiales,and Methanosarcinales accounted for nearly 100%.The distribution at the genus level was significantly different,with Clostridium,Clostridium＿sensu＿stricto,and Petrimonas being the dominant bacterial genera in spring,summer,and autumn and winter,respectively.As for the archaea community,Methanobrevibacter in spring and autumn,Methanosaeta exclusive in summer,Methanoculleus were dominant genera in winter.Except for summer,hydrogenotrophic methanogens existed widely,and the reactor mainly uses a hydrogenotrophic way,suggesting the reactor may have certain resistance.There were a lot of acetoclastic methanogens Methanosaeta in the ADS in the summer.When inoculating summer sludge for AD of different substrates,it could not only maintain a good operating efficiency of the reactor but also increase the methane yield.Conclusions: The core microbe communities of AD reactors with long-term stable operation had great similarity at a greater taxonomic level.In autumn and winter,the ADS had more suitable VS,C/N,and diversity.However,the hydrogenotrophic methanogenesis pathway was mainly used.Looking back at the ADS in summer,methanogenic archaea which dominated the acetoclastic methanogenic pathway were abundant,and excellent results of digestion were obtained in practice.Combined with the functional understanding and comprehensive application of microorganisms,according to the C/N of the substrate,OLR,and operating conditions,the stable operation of the AD reactor and the purpose of improving methane yield can be achieved,and the dual benefits of environment and economy can be realized.