Study On The Process Of Post Nitrogen Removal Filter Based On Partial Shortcut Denitrification Coupled With Anaerobic Ammonia Oxidation

The deep denitrification unit of sewage treatment plant generally has the problem of low biodegradable COD content in the influent and the need for additional carbon source,which not only increases the operation cost,but also has the risk of exceeding the effluent COD.The short-range denitrification coupled anaerobic ammonia oxidation process has the advantages of saving carbon source,no aeration and low sludge yield.However,due to the low concentration of tailwater matrix,its application in deep denitrification still faces many challenges.In this study,part of the effluent from the grit chamber and the secondary sedimentation tank were mixed and directly introduced into the denitrification filter,and the effluent from the grit chamber was used to provide carbon source to obtain the water quality suitable for short-range denitrification anaerobic ammonia oxidation reaction.Through experiments,the effects of water distribution ratio,HRT and filter material on the operation performance of denitrification filter were investigated,the process operation parameters were optimized,the partial short-range denitrification coupled anaerobic ammonia oxidation deep denitrification process was successfully constructed,and the process efficiency,stability and applicability were analyzed.The denitrification activity of biofilm was measured by kinetic test,the contribution rate of anaerobic ammonia oxidation reaction to TN removal was calculated,and the nitrogen conversion pathway in the reactor was clarified.Scanning electron microscopy and high-throughput sequencing were used to analyze the biofilm morphology and microbial community structure,and analyze the denitrification mechanism.This study can provide ideas for the transformation of traditional denitrification deep denitrification process in sewage treatment plant.The main conclusions are as follows:（1）Based on the effluent quality of grit chamber and secondary sedimentation tank of a sewage treatment plant in Zhengzhou,the optimal water distribution ratio and HRT are determined to be 2.5/10 and 14h respectively.Under this working condition,the influent NH₄⁺-N,NO₃^--N and COD concentrations are 10 mg/L,12mg/L and 55 mg/L respectively.Among the three reactors,the reactor filled with manganese sand has the best operation performance.The average effluent TN concentration is 2.31 mg/L,TNLR is 0.038 kg/（m³·d）,and TNRR is 0.034 kg/（m³·d）.The results of short-term impact load test show that the process has strong resistance to the changes of hydraulic conditions and influent load,and the effluent quality always meets the first-class a standard under impact load.The above test results show that the partial short-range denitrification coupled anaerobic ammonia oxidation deep denitrification process constructed in this study has high efficiency and stability.（2）Based on the law of mass conservation,the denitrification path is analyzed,the material balance equation is listed,and then the calculation model of the optimal water distribution ratio is established.The model establishes the relationship between the static outlet water quality of grit chamber and secondary sedimentation tank in the test process and the dynamically changing water quality in the actual project.For the changing outlet water quality of grit chamber and secondary sedimentation tank,the optimal water distribution ratio obtained by the model can adjust the mixing ratio of them in time.This study has general guiding significance for the transformation of traditional denitrification deep denitrification process.（3）The physical and chemical characteristics（roughness and specific surface area）of filter material determine its adsorption performance and microbial growth environment,and then affect the operation performance of the reactor.Zeolite and manganese sand are more conducive to microbial growth than quartz sand.The biofilm coverage rate is fast,and the adsorption performance is better than quartz sand.They show better operation performance when the biofilm is not fully formed.The biofilm morphology and microbial community structure formed by different filter materials are also different.The biofilm morphology and structure of quartz sand is loose and the renewal rate is fast.The biofilm of zeolite and manganese sand is distributed in a"honeycomb"shape,with compact structure and better stability than quartz sand.（4）The denitrification function of dominant bacteria in each reactor was analyzed.The sum of relative abundance of dominant denitrifying bacteria in each reactor is 19.54%,13.22%and 15.16%respectively.There is a kind of bacteria aridibacter which lacks nitrite reductase and can only reduce NO₃^--N to NO₂^--N.The dominant anammox genera are Candidatus Brocadia and Candidatus Kuenenia,and the sum of relative abundance is 0.25%,0.26%and 1.52%respectively.It shows that quartz sand is more conducive to the screening of denitrifying bacteria,and manganese sand is more conducive to the enrichment of anaerobic ammonia oxidizing bacteria.The dominant nitrifying bacteria are Nitrospira and Comamonas,with low relative abundance,which is consistent with the measured results of biofilm denitrification activity,indicating that the denitrification process in each reactor is mainly partial short-range denitrification coupled with anaerobic ammonia oxidation,and there are also nitrification and denitrification.