Advanced Denitrification Efficiency Of Municipal Wastewater Based On Iron Autotrophic Denitrifying Microorganisms

At present,water eutrophication caused by nitrate nitrogen（NO₃^--N）pollution is still in urgent need of solution.Traditional biological nitrogen removal technology requires the addition of additional organic carbon sources,resulting in secondary pollution and other problems,resulting in limited total nitrogen removal rate,and the secondary effluent nitrogen concentration of urban sewage treatment plants is far higher than the eutrophication limit.Therefore,It is necessary to explore appropriate technology for advanced denitrification treatment of secondary effluent.Autotrophic denitrification technology has become a hot spot in denitrification research at present.Due to its advantages of less secondary pollution and low sludge yield,autotrophic denitrification technology has attracted wide attention.Among them,electron donors of iron autotrophic denitrification are easy to obtain and the cost is low.Based on the above,a new technology for iron autotrophic denitrification of low carbon ratio wastewater was developed to analyze the influence of appropriate electron donors and different environmental factors on iron autotrophic denitrification,and to analyze the diversity and metabolic function of microbial community in autotrophic denitrification.Finally,a reactor was constructed to treat simulated secondary effluent.To provide a theoretical basis for the practical application of iron autotrophic denitrification technology,the research contents and results are as follows:A group of iron autotrophic denitrifying mixed bacteria with efficient denitrification function were obtained by enrichment and acclimation from corroded sewage pipes.By monitoring the denitrification efficiency and pH value changes,the best denitrification efficiency of different kinds of electron donors(zero-valent iron,siderite and Fe²⁺)was investigated to select the best electron donors for subsequent experiments.The experimental results show that when zero-valent iron is the electron donor,the optimal efficiency is as follows:TN removal rate is about 95%.The autotrophic denitrification process with Fe substrate as electron donor was further constructed.The effects of dissolved oxygen,pH,Fe²⁺and iron powder dosage on the denitrification efficiency of the iron autotrophic denitrification system were explored by monitoring the concentrations of NO₃^--N,NO₂^--N,NH₄⁺-N and TN as well as pH changes.The results show that dissolved oxygen has the greatest effect on the growth of microorganisms.The nitrogen removal efficiency was higher when pH value was 6.5 and 7.5,and the total nitrogen removal rate was the highest at 76.3%.In summary,the denitrification efficiency of iron autotrophic denitrification can reach96%under the optimal conditions.Building a secondary reactor process simulation,through the analysis of nitrogen concentration change in each stage of the reactor operation efficiency of denitrification,using scanning electron microscopy（sem）analysis of iron powder on the surface of bacteria adhesion and REDOX conditions for iron powder in the process of denitrification changes,analysis of microbial community structure by denitrifying bacteria in the process plays a leading role.The experimental results showed that the removal efficiency of TN in the reactor was slowed down due to the high nitrogen load,and the surface of iron powder in the reactor was seriously oxidized and attached with bacterial micelles formed by denitrifying bacteria.Proteobacteria,Acidobacteria and Bacteroidetes with relatively high abundance were found to be the bacteria with the highest relative abundance,and Subgroup 6 was the key bacteria for the conversion between nitrate nitrogen and nitrite nitrogen.This study provides a theoretical basis for the practical engineering application of iron autotrophic denitrification technology and is helpful for the advanced treatment of secondary effluent in urban sewage treatment plants.