| Nowadays,nitrogen has become the main pollutant of water pollution.There is plenty of N-containing wastewater in environment,which cause eutrophication of water.Therefore,nitrogen removal is one of the most urgent problems in the field of wastewater treatment.Wetland sewage treatment system is anenvironmental-friendly wastewater treatment process and an effective alternative to traditional sewage treatment system.However,different types of wetlands have different pathwaysto remove nitrogen,and the nitrogen removal capacity of wetlands is also affected by external conditions.This paper explores the nitrogen removal pathways of different wetlands and the influence of environmental factors on the denitrification capacity of wetlands.Methane is a greenhouse gas.Methanotrophs are classified into aerobic methanotrophs,anaerobic methanotrophs and facultative methanotrophs.Aerobic methanotrophs are widely distributed in rice filed,landfills and freshwater sediments,etc.Wetlandsediment is inanoxic or anerobic condition,and issuitable for the survival of methanogenic bacteria,so it can emit a large amount of methane.At the same time,there are many kinds of methane-oxidizing bacteria in the wetland substrate.Aerobic Methanotrophs in different wetland substrates were investigated by Microbial analysis of different wetland substrates.Then,the reactor was carried out to verify weather aerobic methanotrophs play a role in the methane oxidation process in the wetland.The possibility of N2O oxidizing CH4 was investigated by enrichment and purification.The conclusions of this paper are as follows:(1)Methane emissions are different in different wetlands.There is almost no methane emission in the natural wetland of the Yellow River Delta(XRD),however,methane is released from the constructed wetlands of Xiaomei River(XMR)and Dongwen River(DWR).This may be related to the different ways of nitrogen removal.Denitrification plays a leading role in YRD,and nitrification dominates in the DWR and XMR.(2)Environment factors such as dissolved oxygen,temperature,and organic matter content have an impact on wetland methane emission and pollutant treatment.The number of aerobic methanotrophs in XMR is greater than DWR,but methane emission is also greater than DWR.In small-scale experiments on methane oxidation,the methane emission of DWR is lower than that of XMR.The result can be attributed to the large pore structure and excellent permeability of DWR matrix,which facilitates the transport of oxygen.In contrast to DWR,the XMR matrix is a compact soil that is not conducive to oxygen transport.The number of denitrifying bacteria in YRD is the least,but the lower DO and higher y-Proteobacteria abundance lead to superior denitrification capacity.More nitrifying and denitrifying bacteria is exhibited in the DWR and XMR,but higher DO and ?-Proteobacteria are more conducive to nitrification.(3)Under anaerobic conditions,aerobic methanotrophsstill exist in the wetlandsubstrates and they belong to Alphaproteobacteria and Gammaproteobacteria.The result indicates that aerobic methanotrophs exist and play the role of oxidizing methane in anoxic environment.CH4 reacts with N2O which act as an electron acceptor in the anoxic conditions.The strains involved in this reaction are mainly type I aerobic methanotrophs,and Methylomonas may be the main genus.The study on nitrogen conversion and methane release in wetlands can serve as a reference for wetland in engineering applications.It is also found that both wetland substrate types and external environments can affect wetland pollutant removal and methane emission.This study provides a basis for the construction and site selection of constructed wetlands.In addition,exploring the existence and role of aerobic methanotrophs in the anoxic environment of wetland matrix and verifying the co-reduction of CH4 and N2O could provide new ideas and methods for greenhouse gases gas emission reduction in the wetland systems in the future. |
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