Mechanism And Application Of Feammox To Nitrogen Removal In The Process Of Agricultural Nitrogen Pollution Migration

Agricultural nitrogen pollution is an important environmental problem in China,the nitrogen which isn't absorbed by the corp at the fertilization process can migrate from the farmland to irrigation ditches,riparian zones,rivers and lakes following surface runoff,and which easily causes lake eutrophication.Nitrogen removal by the microbial process is an important way to solve the nitrogen pollution.A new microbial process of anaerobic ammonium oxidation has been recently described in which NH₄⁺is oxidized to NO₃^-,NO₂^-and N₂ and where the main associated reaction is Fe(III)reduction(termed Feammox).This new discovery has changed old cognition of nitrogen cycle and de veloped a new direction about nitrogen removal.Ho wever,the questions about the contribution,mechanism and application of the Feammox process on nitrogen removal following nitrogen pollution migration in the agriculture area(from paddy to irrigation ditches/lake riparian and lake;from surface soils to deep soils)have not been systematic study.Conducting researches on this aspect can effectively fill in related blank and clearly understand the contribution of the Feammox process in nitrogen removal.To address these problems,we selected the soil and sediment in the road of nitrogen pollution migration in a rice-wheat rotation area(Wanshandang Lake)of the Taihu Lake region in China as the study area.Based on field investigation,laboratory simulation and enrichment culture,the main objectives of this study were to analyse the contribution of Feammox in the soil/sediment of paddy,irrigation ditch,lake riparian and lake zones,and evaluate the influence of environmental factors on the Feammox process,and enrich related microbes,and explore the mechanism of the Feammox on nitrogen pollution removal,and excavate application value of the Feammox process on nitrogen pollution removal,by using a ¹⁵N-labelled isotope tracing technique and analysis of microbial communities,.The main research results are as follows:(1)Contribution of Feammox to nitrogen removal in the process of agricultural nitrogen pollution migrationFeammox process could be found in all soils and sediments of each land used types of this rice-wheat rotation area.Feammox rate ranged from 0-0.50 mg N kg^-1d^-1.About 28.43-113.68 kg N ha^-1year^-1 of nitrogen pollution was removed by the Feammox process in the surface soil/sediment(0-10 cm)of this area.The contribution sizes of nitrogen pollution removal between the paddy,irrigation ditch and lake riparian were different following the change of the season,and which was higher than that in the lake sediment.In the soil profile of the paddy,the active layer of Feammox activity was distributed in the depth of 20-30 cm.The Feammox rate of the summer was significantly higher than that in the winter.The combined TOC content,Fe(III)content and Fe(II)content accounted for70.00%of the variation of the Feammox rate(0-10 cm).In the soil at the spring,summer and autumn,the denitrification process was the largest contributor of N₂ produced in surface soil(0-10 cm),accounting for92.26-99.95%of the total N₂ production,while the remainder was due to Feammox.The Feammox process was the main contributor of N₂ produced in the winter and deeper soil,accounting for 40.52-90.20%of the total N₂ production.Therefore,the Feammox process plays an important role on nitrogen pollution removal in the road of agricultural nitrogen pollution migration.(2)Mechanism of Feammox to nitrogen removal in the process of agricultural nitrogen pollution migrationWhen the addition of ammonium fertilizer was 100 kg N ha^-1 year^-1and 200 kg N ha^-1 year^-1,and the addition of phosphate fertilizer was 50 kg N ha^-1 year^-1,the soil Feammox rate could be promoted.But using higher concentration of ammonium fertilizer(400 kg N ha^-1 year^-1)and nitrate fertilizer(100 kg N ha^-1 year^-1)could inhibit the soil Feammox rate.The inhibited effect of using nitrate fertilizer on the Feammox rate would be weakened as the time went on.The imidacloprid at the concentration of 5 mg kg^-1 could reduce the Feammox rate at the initial stage,and while in the long run,using one time or multiple times of the imidacloprid would not impact on the Feammox process.The treatment of adding 2%,5%straw and water extract of the straw could promote the soil Feammox rate.Fe Cl₃,Fe₂O₃,Fe₃O₄ and Fe(OH)₃ all could accelerate the soil Feammox process in appropriate proportion.At the low concentration of NO₃^-and NO₂^-treatment,the soil Feammox rate was promoted,and but the soil Feammox rate was inhibited at the higher concentration.At the enrichment system of Feammox bacteria used the soil as inoculum,the efficiency of NH₄⁺removal was improved by Feammox process after continuous culture,and the community structure of the bacteria were also changed.Relative abundances of Unclassified(p?Proteobacteria),Geothrix and Pseudomonas were significantly improved.The Feammox bacteria were suitable to grow in a micro acid environment,and used inorganic carbon as carbon source.Adding AQDS could promote the Feammox rate in the reactors.Feammox bacteria had an ability to achieve extracellular electron transfer.(3)Application evaluation of Feammox bacteria on nitrogen removalBased on the simulative demonstration of different ecological restoration measures on nitrogen pollution removal,the result showed that adding the Feammox bacteria could optimize river sediment microbial community,and improve the ability of removal nitrogen.Feammox rate of the deep sediment was increased by 136.07%at the treatment of adding related Feammox bacteria.Planting Myriophyllum spicatum and adding the biochar could promote nitrogen removal in the water and surface sediment.Planting Myriophyllum spicatum could reduce 31.58%of the total nitrogen and 33.05%of NH₄⁺to compare to the blank treatment.Using the biochar increased the abundance of denitrification and iron reduction bacteria,and also enhanced the rate of denitrification and Feammox process.The technology of combined biochar,Myriophyllum spicatum and Feammox bacteria could effectively remove the nitrogen in the river water and sediment.The removal rate of TN of the river water and the removal rate of NH₄⁺of the river sediment were respectively enhanced by 53.38%and 44.16%due to using this technology.Therefore,using the Feammox bacteria and Feammox process to solve nitrogen pollution of the sediment has a good feasibility,and while this technology used in situ river should make further explorations.