Based On Carbon-biological Carrier To Investigate The Mechanism Of Anammox Nitrogen Removal Process

Conventional nitrification and denitrification-based techniques consume large quantities of energy and easily cause secondary pollution.It is difficult to achieve a balance between nitrogen removal efficiency and economic benefit.Anaerobic ammonium oxidation（anammox）is an efficient and autotrophic biological nitrogen removal technique developed in two decades.However,this technique also has some limitations,for instance,the low cellular yield of anammox bacteria results in its long doubling time,the electron acceptor NO₂^--N is difficult to obtain,and product some byproduct NO₃^--N during the nitrogen removal process.As the performance of carbon-based materials could promote the traditional denitrification process,this study is focus on:（1）Batch experiments were used to explore adding different biological carriers to the nitrogen removal activity of anammox bacteria.It found that biochar（made from wood,coconut shell,and coal）can promote the nitrogen removal performance of anammox process,but the biochar leachate has no significant effects.The redox-sensitive chemical groups are abundant on distinct biochar surfaces,which have the capacity of electron-donating and electron-accepting.The functional groups-mediated electron transfer contributes to the decreased accumulation of nitrate of the anammox process.In addition,the biochar acts as a buffer to stable pH values of the aqueous environment,makes the circumstances more suitable for the growth of anammox bacteria.Sequencing results demonstrated that Candidatus＿Jettenia and Candidatus＿Brocadia are dominated in the microbial community.More genes involved in the anammox process are expressed,thereby improving the total nitrogen removal efficiency of the anammox process.Adding biochar as a biological carrier in the anammox process provides an efficient method to reduce the accumulation of NO₃^--N.（2）Based on the study in the previous chapter,in order to reduce the limitation of operating conditions for process with a single functional microorganism,this study uses iron-activated carbon materials（Fe/AC）as biological carriers to start up a continuous-flow anaerobic expanded granular sludge blanket reactor（EGSB）,an autotrophic biological nitrogen removal system integrating anaerobic ammonium oxidation coupled to iron（Ⅲ）reduction（Feammox）and anammox processes was successfully operated.During the stable operational period,the total nitrogen（TN）removal efficiency reached 82.9%±6.8%with a nitrogen removal rate of 0.46±0.04 kg-TN/m~3/d.The contributions of the Feammox,anammox and heterotrophic denitrification pathways to TN loss accounted for 7.5%,89.5%and 3.0%,respectively.The biological nitrogen removal batch experiments showed that AC could accelerate the anammox rate and the Feammox rate.Using Fe/AC as a biological carrier provides a promising method for starting up the autotrophic biological nitrogen removal reactor with high-efficiency nitrogen removal.（3）In summary,this study demonstrates that using biochar as a biological carrier can accelerate the extracellular electron transfer process with microorganisms and promote the redox reaction of nitrogen.Using Fe/AC to start up the anammox nitrogen removal system integrating Feammox,anammox and heterotrophic denitrification pathways,which can improve the TN removal efficiency of the biological nitrogen removal system.Both types of biological carriers provide a promising method to promote the application of the anammox process.