Enrichment Of PAHs-degrading Methanogenic Cultures And Study On Enhancing PAHs Anaerobic Methanogenic Degradation

The study of PAHs anaerobic degradation under methanogenic condition can offer important guidance for evaluating PAHs fate in anaerobic environments and for PAHs pollution remediation under anaerobic conditions,but little is known about microbial composition and degradation characteristics under this condition.In this study,we focused on investigating the effects of initial environment source and PAH types on degrader composition,we also explored PAHs degradation potentials,degradation pathways and degradation improvement methods,with an aim to better understand PAHs fate in typical anaerobic surroundings and to provide theoretical support for PAHs pollution control.Characterization of a phenanthrene-degrading methanogenic community intiated from mixed environments(anaerobic sludge,coke wastewater and oil-contaminated soil)revealed that phenanthrene degradation rate in the mixed environment was greater than that in sediments;the ability of methane production was poor and the actual methane conversion rate was 1%;different compounds had different impacts on phenanthrene degradation rates,with chain hydrocarbons having the most positive effects.Illumina sequencing demonstrated that bacterial populations were mainly associated with Comamonadaceae and Nocardiaceae,and that methanogenic archaea groups were dominated by Methanobacterium and Methanothermobacter,which were different from those from sediments,indicating that initial environment source had significant impacts on PAH degrader composition.Molecular characterization of five PAH-degrading methanogenic communities and related degradation pathways demonstrated that PAH types significantly changed microbial populations.The dominant bacterial and archaeal populations of two-ringed PAHs were similar.The dominant degrading bacteria of three-ringed PAHs were different,and their archaeal members were quite different.Degradation communities of fluoranthene were different from others' and showed greater diversity.Substrate utilization tests showed that naphthalene-degrading culture could degrade 2-methyl naphthalene,and vice versa.The degradation cultures of phenanthrene,anthracene and fluoranthene could merely degrade the PAH used in enrichment phase,which mightbecause their diverse degrading microbes or degradation pathways.The metaboliteanalysis showed that the degradation pathway of two-ringed PAHs were quite similar,both could be through carboxylation reaction,which was consistent with their similar community structure.The investigation of the potential mechanism of magnetite facilitating phenanthrene anaerobic methanogenic degradation indicated that the positive effects of magnetite on phenanthre degradation rate(25.1%)was only found when methanogenesis was smooth,and that magnetite showed good chemical stability during the incubation time.QPCR results showed that methanogen abundance in our enrichment consortium did not increase in the presence of magnetite,but microbial electron transporting system(ETS)activity significantly enhanced.Considering the syntrophic degradation of phenanthrene,we inferred that the improved effect of magnetite here might also be attributed to its role as electron conduits between phenanthrene-degrading bacteria and methanogens.