Effect Of Sponge Iron Dispersion On BSIS Anaerobic And Aerobic Microenvironment And Simultaneous Nitrification And Denitrification Characteristics

Studies have found that adding functional carriers can transform the activated sludge process into a mud-film mixing process and significantly improve the denitrification performance of the system.The previous research of the research group found that the Biological Sponge Iron System（BSIS）has strong denitrification performance.The BSIS is composed of adding sponge iron to the activated sludge system in a certain way under sufficient oxygen conditions.At the same time,it was found that the oxygen absorption corrosion of sponge iron consumes the surrounding dissolved oxygen,and an anoxic and anaerobic microenvironment can be created in an aerobic environment.It is speculated that a simultaneous nitrification and denitrification process may occur inside the system.However,there are few reports about the distribution of dissolved oxygen in the biological sponge iron system,the characteristics of anaerobic and aerobic microenvironment,and simultaneous nitrification and denitrification.The size of the sponge iron spheres will directly affect the distribution of dissolved oxygen in the biological sponge iron system,anaerobic and aerobic microenvironment characteristics,and then directly affect the denitrification effect of the entire biological sponge iron system.So in this study,simulated domestic sewage was used as the research object.The changes of dissolved oxygen in the biological sponge iron system and the characteristics of anaerobic and aerobic microenvironment under different dispersion degrees（The surface area per unit mass of sponge iron exposed to aerobic area）were investigated.At the same time,the effects of different dispersion degrees on the denitrification performance and iron leaching amount of the biological sponge iron system were investigated.The enzyme activity of the biological sponge iron system with different dispersions was measured,and the high-throughput sequencing technology was used to analyze the changes in the composition of the microbial community structure in the biological sponge iron system mixture,the surface of the sponge iron sphere and the internal biofilm.The characteristics of simultaneous nitrification and denitrification in the system were also studied.By measuring the dissolved oxygen inside the sponge iron sphere of the same reactor in different cycles,it is found that the dissolved oxygen concentration inside the sphere is relatively high at the beginning of the measurement in the first cycle of the reactor operation.With the extension of the measurement time,the dissolved oxygen inside the sphere continuously decreases and finally reaches equilibrium.For spheres of the same size in the same reactor,with the extension of the operating time of the reactor,the time for the formation of anoxic and anaerobic microenvironment within the reactor sphere within one cycle is continuously shortened to zero.Different degrees of dispersion have a greater impact on the distribution of dissolved oxygen in the spheres of the biological sponge iron system.In the early stage of reactor operation,the smaller the diameter of the sponge iron ball,the shorter the time to reach a stable anoxic anaerobic microenvironment,and the greater the internal dissolved oxygen.In the middle of the reactor operation,the reactors with different dispersion degrees have different obvious fluctuations.In the later stage of operation,the reactors reached equilibrium within 30 minutes or even less.When stable,the dissolved oxygen concentration in the spheres with different dispersions all was 0.02 mg/L.Through real-time monitoring of the distribution characteristics of dissolved oxygen in the sponge iron spheres,it is found that a stable aerobic,anoxic,and anaerobic microenvironment can be formed inside the biological sponge system after a certain period of time.It is conducive to the synergistic symbiosis of aerobic,anaerobic and facultative microorganisms in the reactor,and will effectively enrich the community structure and microbial diversity in the system.By studying the effect of different dispersion on the removal effect of biological sponge iron system,it is found that the dispersion of sponge iron has little effect on the removal effect of CODcr,NH₄⁺-N and the accumulation of NO₂^--N in the system,but has a great effect on the removal of NO₃^--N and TN.The average removal rate of CODcr for BSIS reactors with different degrees of dispersion is above 94%,and the average removal rate for NH₄⁺-N is above 97%.Both meet the discharge requirements of CODcr and NH₄⁺-N in the sewage level A discharge standard.The concentration of NO₂^--N in the effluent from each reactor fluctuates slightly but always remains at a low level.Among them,the biological sponge iron system reactor with a dispersion of 1.676 cm²/g has the best denitrification performance.The average effluent concentration of NO₃^--N is 13.85mg/L,the average removal rate of TN is80.65%,and the average TN effluent concentration is 14.95mg/L,which meets the TN discharge requirements of the sewage level A discharge standard.Different sponge iron dispersion has a great influence on the iron dissolution of the system.Under aerobic conditions,the Fe²⁺dissolved by the corrosion of sponge iron exists in the form of flocs or precipitates.Comparing the TFe and Fe²⁺concentrations of the biological sponge iron system and the single sponge iron system,it is speculated that the biological sponge iron system may undergo a nitrate-dependent ferric oxidation process.Different sponge iron dispersion has a greater impact on the denitrification enzyme activity of the system.The addition of sponge iron effectively enhances the enzyme activities related to the nitrification and denitrification process of the system.The key enzyme in the biological sponge iron system reactor with a dispersion degree of 1.676 cm²/g,especially the increase of NAP enzyme activity directly related to aerobic denitrification,which showed a good agreement with the high-efficiency removal of total nitrogen,and confirms that the biological sponge iron system has SND phenomenon.High-throughput sequencing analysis of ordinary activated sludge system,biological sponge iron system mixture,internal and external biological membranes of sponge iron spheres found the existence of anaerobic bacteria phyla,such as Bacteroidetes,Patescibacteria,Actinobacteria and Chloroflexi,multiply in the biological sponge iron system,confirming that the system has an anaerobic environment.The existence of some typical aerobic denitrifying bacteria and nitrate-dependent ferrous iron oxidizing bacteria such as Acinetobacter,Arenimonas,Hydrogenophaga,Rhodoferox,Thermomonas and Inhella confirms the SND process of biological sponge iron system.That also provides strong evidence for the stronger denitrification performance of the biological sponge iron system.