Mechamism Study For Enhancement Of ZVI-dependent Nitrate Reduction By Anammox Bacteria

The Fe⁰/Fe²⁺-dependent nitrate reduction by anammox consortia extends the recently discovered versatile metabolisms of Anammox bacteria..However,the current research focusing on this phenomena is still limitted.There is less attention on the nitrate transformation pathway,the role of Anammox bacteria and the changes of microbial community.in this process.In this thesis,batch experiments were conducted to compare the effects of adsorption of NH₄⁺and Anammox bacteria on the reduction rate of NO₃^-in Fe⁰/NO₃^-systemand investigate the role of anammox bacteria in NO₃^-reduction by Fe²⁺leached from Fe⁰without chemical reaction occurrenceContinuous-flow reactors were conducted to explore the control strategy to achieve the long-term stable operation of Fe⁰-dependent nitrate reduction by anammox consortia,which can support cultivation of Anammox bacteria..Further,the expression of functional genes narG,napA and nrfA and the changes of microbial community structure were determined by real-time fluorescence quantitative PCR and high-throughput sequencing.Through the above evaluations,the transformation pathway of nitrate,the role of Anammox bacteria in nitrate conversion and the characteristics of microbial community were elucidated.change Meanwhile,the key influencing factors in this process were also investigated.The main conclusions were as follows:?1?The stable Fe⁰-dependent NO₃^-reduction by Anammox consortia in a continuous-flow reactor was achieved.The results showed that the functional genes napA and nrfA were significantly expressed,indicating that Anammox bacteria could use Fe²⁺dissolved from Fe⁰to dissimilatory reduce NO₃^-to NH₄⁺.?2?Nitrate reduction,dissimilatory nitrate to nitrite and dissimilatory nitrite to ammonia were the main bioreduction pathways of nitrate.These were also the main ways for Anammox bacteria to obtain ammonia and nitrite.The removal of nitrate was realized under the combined actions of the above biological processes.?3?The relative abundance of Candidatus Brocadia and Candidatus Jettenia increased during the long-term operation,indicating that Candidatus Brocadia and Candidatus Jettenia could adapt to the environment containing Fe⁰and nitrate.?4?To maintain the adequate activated Fe⁰and to eliminate the adverse effects of Fe⁰passivation are vital for the sustainable and stable operation.The nitrate removal efficiency and the sustainability of reactor could be enhanced significantly by regular renewal of fresh Fe⁰powder.The average removal efficiency of nitrate and total nitrogen were 75.00%and 54.02%,respectively.?5?The effects of iron form,Fe/N ratio,pH and temperature on this process were investigated.The iron form,reaction temperature and Fe/N ratio had a significant effect on the nitrate reduction.The nitrate removal rate was over 88.00%with temperature of 35?C,Fe/N ratio of 38.23 and pH of 4.0 when nano-Fe⁰serving as electron donor.The present study confirms and further extends the recently discovered versatile metabolisms of Anammox bacteria,also it can help to in-situ circumvent the accumulation of nitrate produced by anammox process itself,thus providing a new options for improving the total nitrogen removal efficiency.