Study On The Construction And Efficiency Enhancement Of Feammox Autotrophic Nitrogen Removal System

Nitrogen（N）is an essential element to maintain life activities on earth.However,excessive application of chemical fertilizers and excessive discharge of nitrogen-containing wastewater have led to serious eutrophication of water.In recent years,Fe（Ⅲ）-mediated anaerobic ammonium oxidation（Feammox）has been widely proved in paddy fields,wetlands and sewage treatment systems.This process does not require aeration or carbon source.If it is applied to nitrogen removal in wastewater,the cost of wastewater nitrogen removal can be significantly reduced.In this study,the soil in natural environment,Anammox granular sludge and activated sludge were used as the research objects.Fe（Ⅲ）was used to stimulate the Feammox potential of relevant functional microorganisms,and the structure and evolution of microbial community during the process of domestication were studied.On this basis,the autotrophic nitrogen removal system of Feammox suitable for sewage treatment was constructed,and its efficiency enhancement was studied.The main research contents and results are as follows:In this study,paddy soil（PS）,wheat-maize rotation soil（WS）and lake riparian soil（LS）were used as the research object,and FeCl₃ was used as the Fe（Ⅲ）iron source to stimulate the Feammox potential of related functional microorganisms in environmental samples.In the first stage（0-56 d）,under the continuous stimulation of Fe（Ⅲ）,the metabolic pathway of Feammox was stimulated in three different soils,but the product types were different.The main product in PS and LS is NO₃^-,while NO₃^-and NO₂^-exist simultaneously in WS.In the second stage（57-84 d）,the effect of nitrogen removal in PS became worse after the cessation of Fe（Ⅲ）addition,but there was still a high nitrogen removal rate in WS and LS,with nitrogen loss rates of 14.8%,45.3%and 36.1%,respectively.These results indicate that nitrate-dependent ferrous oxidation process（NDFO）with Fe（Ⅱ）as the electron donor may occur in the system.The results of microbial community analysis showed that the addition of Fe（Ⅲ）led to the increase of Fe BR（Geobacter）abundance,namely,Fe（Ⅲ）iron source stimulation can stimulate the Feammox potential of related microorganisms in soil environment.Taking Anammox granular sludge as the object,Fe₂O₃ was identified as the iron source to stimulate the Feammox potential of Anammox granular sludge through batch experimental.Based on the batch experiment,the long-term experiment of the UASB continuous flow reactor was further carried out.By adding Fe₂O₃ and gradually reducing the ratio of NO₂^--N to NH₄⁺-N in the influent,the concentration of NH₄⁺-N and TN in the effluent of the experimental group R2 was significantly lower than that of the control group R1.By XPS analysis,it was found that Fe（Ⅱ）accounted for up to 61.75%of the solid iron minerals in the R2 reactor,which indicated that the Feammox pathway occurred in the reactor R2.Through16Sr DNA microbial community sequencing,it was found that obvious enrichment of the Fe RB（Pseudomonas）appeared in the R2 reactor.These results indicate that the Feammox potential of related microorganisms in Anammox granular sludge can be activated by adding Fe₂O₃ and gradually reducing the ratio of NO₂^--N to NH₄⁺-N,and the Feammox autotrophic nitrogen removal system suitable for sewage treatment can be constructed.Flocculation sludge and anaerobic digestion sludge were used as objects,and Fe₂O₃ was added to stimulate and acclimate them.The removal rate of NH₄⁺-N and TN was about42.70%-48.06%and 34.63%-38.30%,and theΔNO₂^--N/ΔNH₄⁺-N was about 1.10.This indicated that the autotrophic nitrogen removal system of Feammox was constructed in the system.By adding AC and gradually increasing the TN load in the influent,under the condition of the influent TN concentration of 200 mg/L and the concentration ratio of NH₄⁺-N to NO₂^--N was 1:1,the TN removal rate reached 89.66%-92.57%,indicating that the addition of AC strengthened the Feammox process and improved the TN removal rate.The results of batch experiments further confirmed that the Feammox nitrogen removal pathway was successfully excited in the system,and the NDFO pathway with Fe（Ⅱ）as the electron donor existed.Microbial community analysis showed that microorganisms with Feammox potential,such as Ellin6067,Fe RB（Pseudomonas）and ADurb.Bin063-1,were obviously enriched in the system.In addition,Ferruginibacter,Terrimonas and other microorganisms with NDFO function also exist.The above results indicated that there was an autotrophic nitrogen removal pathway of Feammox coupled with NDFO in this system.