Efficiency And Mechanism Of Activated Carbon Materials In Enhancing Autotrophic Iron Driving Biological Nitrogen Removal

Nitrogen pollution is an important regional and global water pollution problem,which is harmful to human health and ecological environment.Heterotrophic biological denitrification has disadvantages,such as high energy consumption of aeration,high carbon source consump-tion and high sludge yield,resulting in resource waste and secondary pollution.Therefore,the process optimization control and microbiological mechanism of autotrophic biological deni-trification have become a research hotspot in the field of sewage biological treatment.Iron（Fe）is the most abundant transition metal in the lithosphere.Iron-driven biological denitrification includes anaerobic iron ammonium oxidation（Feammox）and iron autotrophic denitrification（IAD）.The reaction process is safe,economical and does not cause secondary pollution,which has a wide application prospect in water treatment.This article examines the effect of activated carbon（AC）as an electronic shuttle（ES）on the denitrification process of Feammox and IAD,and investigates the influence of different environmental factors on the iron-driven biological denitrification process.The main research contents of this thesis are as follows:（1）Analysis of the mechanism of activated carbon to promote anaerobic iron ammonium oxidation reaction.In the 150-day EGSB reactor,the volume load ratio（VLR）is 0.04–0.06 kg N m^-3 d^-1,the removal rate of NH₄⁺-N reaches 90.9%–99.5%.The formation of secondary iron minerals and the enrichment of IRB together indicate the occurrence of the Feammox process.The batch experiment results showed that when wood AC was used as ES,it had higher catalytic performance,and the TN removal rate was 85.7%.Electrochemical and Fou-rier transform infrared spectroscopy analysis showed that the oxygen-containing functional groups of activated carbon had electron transfer ability.In addition,Fe（Ⅱ）/Fe（ⅡI）species and secondary iron minerals were also found in the system.In this system,wood AC promoted iron circulation and thus facilitated denitrification.Microbiological analysis showed that in the complete Feammox system,the high abundance of Proteobacteria and Acidobacteriota play an important role.Electrons are primarily generated from the oxidation of NH₄⁺-N by IRB,and AC with quinone C=O and phenolic-OH groups accelerate electron transfer from IRB to solid iron minerals.This study provides a method for enhancing Feammox process mediated by wood AC,which has important engineering application potential for the devel-opment of autotrophic biological nitrogen removal technology.（2）The influence of different conditions on the AC-mediated anaerobic iron ammonium oxidation reaction and mechanism analysis.In batch experiments,the effects of p H,nitrogen concentration,DO content,Na HCO₃ and Mg SO₄ concentration on the efficiency of Feammox denitrification mediated by wood AC were studied.The results showed that:p H around 6–7was more beneficial to promote the wood AC-mediated Feammox denitrification process.The system was in a neutral and acidic condition,and the microorganisms secreted EPS and other substances,which may promote bioaccumulation,and the microorganisms work together to promote the denitrification rate of the Feammox process.When the initial nitrogen concentra-tion was 30 mg L^-1 Feammox’s NH₄⁺-N removal rate reached 73.77%,TN removal efficiency was 69.28%;when Na HCO₃ concentration was 250 mg L^-1,NH₄⁺-N removal rate reached94.65%,TN removal rate was 91.38%;when the sulfate concentration was 150 mg L^-1,the highest removal rates of NH₄⁺-N and TN were 99.01%and 96.05%,respectively.DO can promote the formation of Fe（ⅡI）so that Feammox can continue to remove nitrogen.（3）The effects of different types of iron mineral and AC on the process of iron autotrophic denitrification.Different types of iron mineral promoted different products of microbial deni-trification.Fe CO₃ and Fe Cl₂ mainly promote the conversion of NO₃^--N to N₂,and when Fe~0was used as an electron donor,it mainly promoted the conversion of NO₃^--N to NH₄⁺-N by microorganisms.In Fe CO₃ and Fe Cl₂,norank＿f＿Gemmatimonadaceae,OLB13,nor-ank＿f＿Saprospiraceae,and norank＿f＿Anaerolineaceae had higher abundance.In the Fe~0group,the dominant bacteria were Erysipelothrix,Shivajiella,Thaurea,norank＿f＿Moraxel-laceae,Paludibaculum.There was not much difference in the removal rate of NO₃^--N and TN in the IAD process when ESs（AC,AQDS）was added and was not added.XRD analysis showed that Fe CO₃ was partially converted toγ-Fe OOH.The microbial community analysis showed the existence of OLB13,Candidatus Brocadia,Gemmatimonadaceae,SBR1031 and other bacteria.OLB13 contains codes for respiratory ammoniation that can interact with Anammox bacteria.OLB13 and Candidatus Brocadia work together to promote microbial denitrification.Gemmatimonadaceae is a denitrifying bacterium that can promote the removal of NO₃^--N.SBR1031 can coexist with Candidatus Brocadia and may be distributed on the outer layer of granular sludge or flocculated sludge to promote nitrogen conversion.The ad-dition of a certain amount of organic carbon can promote the oxidation of Fe（Ⅱ）by microor-ganisms and the removal of NO₃^--N.