The Impact Of Addition Of Iron Oxides On Anaerobic Methanogenic Acetate Degradation At The Thermophilic Environment

High conversion of short chain fatty acid(Acetic acid,Propionic acid,Butyric acid)is one of the key steps in the anaerobic methanogenic process of organic matter and iron oxide is able to promote such process.Furthermore,under the methanogenic environment,there is a complex relation(synergy or inhibition)among iron reducing bacteria,fatty acid oxidizing bacteria and methanogenic archaea.Therefore,it is necessary to quantitatively analyze their growth competition.In this paper,the brewery sludge and paddy soil were used as the inoculated methanogenic microorganism,sodium acetate was set as a substrate at 50℃for the anaerobic digestion.The relative relationship between acetic acid oxidizing bacteria and iron reducing bacteria at high temperature with different iron oxides was studied by Illumina high-throughput sequencing technology.Combining the quantitative PCR experiment with analysis of PCA and RDA,the relationship between fatty acid oxidizing bacteria and iron reducing bacteria was accurately quantified and the effect of environmental factors were investigated.The dominant methane-producing pathway and the rate of methane-producing pathway were determined by electron flow calculation.And the interaction relationship dominated in the methane-producing system were discussed.The result was shown as below.(1)At the methanogenic system with sludge,the addition of goethite and hematite promoted methane production.The addition of goethite and hematite significantly increased the maximum methane production rate of the system(p<0.05).The microbial community analysis showed that the relative abundance of fatty acid oxidizing bacteria in the mineral group was higher than that in the control group.The major fatty acid oxidizing bacteria was syntrophaceticus.The major methanogenic archaea detected in the four groups was Methanobacterium,methanogenic archaea(Methanobacterium and Methanoculleus)were mainly detected in the Ferrihydrate,goethite and hematite group.Methanobacterium and Methanosarcina were detected in the control group.Quantitative PCR results showed that Syntrophaceticus had a competitive advantage over Geobacter.(2)At the methanogenic system with paddy rice,the results showed that the goethite group and hematite group promoted the methane production rate.The microbial community analysis showed that Syntrophaceticus was the main acetic acid oxidizing bacteria detected in the three groups.The relative abundance of acid oxidizing bacteria was increased with the addition of goethite and hematite.The main iron reducing bacteria detected was Thermincola.The addition of goethite and hematite did not increase the relative abundance of thermophilic iron reducing bacteria.The methanogenic archaea detected in control group and goethite group was Methanoculleus which is a hydrogen methanogen.Hematite group detected major methane-producing archaea were Methanoculleus,Methanothermobacter.Quantitative PCR results showed that Syntrophaceticus had a competitive advantage over Thermincola.(3)The electron transfer rate mediated DIET with goethite and hematite was about10~6 times of that generated by interspecies hydrogen transfer.The interaction between fatty acid oxidizing bacteria and methanogenic bacteria in the anaerobic methanogenesis system competed out the interaction between iron reducing bacteria and methanogenic bacteria.