Study On Transformation Mechanism Of Nitrogen And Sulfur Pollutants In Wetland By Synergistic Effects Of Oxygen Released From Vallisneria Natans And Microbiology

In recent years,with the development of the regulation of black and odorous water bodies in China,the vast majority of black and odorous water bodies have been treated.However,some water bodies have low Dissolved oxygen（DO）and high concentrations of nitrogen and sulfur and other pollutants,leading to the risk of black and odorous water bodies.Therefore,in the future,the focus of governance of black and odorous water bodies in China will change to long-term maintenance of water quality after restoration,and the in-situ self-purification function of river ecology will be strengthened through ecological restoration technology.Submerged plants can effectively improve the water environment,improve the diversity of the ecosystem,and thus strengthen the load resistance of the system to exogenous pollution,it has gradually become a highly efficient,stable and energy-saving treatment technology.In this study,nitrogen and sulfur pollutants in river ecosystem were taken as the main research object.The boundary conditions for the generation of S^2-and H₂S were explored through the sulfate reduction characteristics o under different aeration conditions and different sulfate concentrations in the river sediments,so as to determine the appropriate sulfate concentration range for the simulated wetland experiment.In the simulation experiments,the contribution of Vallisneria natans to the enhancement of in-situ self-purification function in the ecosystem was studied from the aspects of the remediation effect as well as the migration and transformation of pollutants.It was based on 16S r RNA microbial sequencing analysis to explore the response rules of functional microorganisms under different pollution in the planted and unplanted system,and attempt to construct the material circulation and microbial action mechanism of ecological remediation in combination with the monitoring of actual ecological remediation projects.（1）The characteristics of sulfate reduction in river sediments under different sulfate concentration and different aeration conditions,as well as the response rules of related microorganisms such as sulfate reducing bacteria（SRB）,were investigated.The results show that the average reduction rate was the fastest(V=18.31 mg L^-1h^-1)when the initial SO₄^2-concentration was 589.68 mg/L without aeration.However,after additional aeration,the reduction of low concentration SO₄^2-was inhibited,and S^2-and H₂S were gradually generated after the suspension of aeration of high concentration SO₄^2-.Microbial sequencing results showed significant differences in microbial community structure under different concentration SO4^2-and different aeration conditions.（2）The effects of different influent concentrations（7.5,15,22.5,30 mg N/L）of NH₄⁺-N on DO were studied in simulated constructed wetland.The migration and transformation of nitrogen and sulfur pollutants and the characteristics of microbial community showed that the recovery rate of DO in planted group was 0.027-0.07 mg L^-1h^-1,the removal rate of NH₄⁺-N was above 90%.When the concentration of DO was less than 1 mg/L and the concentration of sulfate was more than 100 mg/L,S^2-accumulated and was converted into Fe S and H₂S.16S r RNA sequencing analysis showed that after 30 days,the microbial diversity in both sediments decreased,while the microbial diversity in leaf biofilm increased by 16.42%,and the abundance of nitrifying bacteria increased most obviously.（3）In the study of practical engineering application,water quality monitoring was carried out in three typical rivers in Guangzhou planted with Vallisneria natans.The water quality of Xinshichong was monitored continuously for 24 hours,and 16S r RNA sequencing analysis was carried out on the sediment,submerged plant leaves and water bodies at different sites.The results showed that Vallisneria natans could effectively deal with the release of endogenous pollution and had a certain removal effect on the input of exogenous pollution.16S r RNA sequencing analysis showed that there were different microbial community structures in sediments,leaves and water in the same reach.Vallisneria natans inhibited the multiplication of Cyanobacteria in water bodies and sediments.Nitrogen and sulfur cycle as well as related functional bacteria had regional distribution characteristics.