Biological Nitrogen Removal By Partial Denitrification Coupled With Anaerobic Ammonia Oxidation

In the process of biological denitrification of sewage,the nitrogen removal effect is not ideal due to the lack of carbon source.The partial denitrification coupled anaerobic ammonia oxidation process can realize the simultaneous removal of nitrogen and organic matter under low C/N conditions.However,the strengthening measures of partial denitrification and ANAMMOX are not sufficient and most of the existing studies are started by inoculating mature denitrification and ANAMMOX sludge.In this study,partial denitrification and ANAMMOX system was constructed by using homologous sludge.In order to study the influencing factors of partial denitrification and ANAMMOX.The mechanism of granular sludge was revealed from its physical characteristics,microbial diversity and bacterial community structure.This study creatively proposed that low-intensity ultrasound and high alkalinity conditions could strengthen partial denitrification,and explored the possibility of domestication of homologous sludge to complete partial denitrification and ANAMMOX respectively.The main research contents and conclusions are as follows:（1）Study on influencing factors of partial denitrification.Batch experiments showed that under the conditions of ultrasonic energy density of 0.1w/ml,irradiation time of 10 min and interval of 24 h,the accumulation concentration of NO₂^--N could be increased by 16.63%compared with the control group;Under the condition of p H11,the accumulation concentration of NO₂^--N was 1.77 times higher than that of the control group.On the basis of batch experiment,when the temperature of continuous short-range denitrification system is 27℃,HRT is 4 h and influent NO₃^--N is 45 mg/L,the accumulation of NO₂^--N can reach 19.28 mg/L and NAR can reach 51%.Low intensity ultrasound and the increase of p H make the surface of granular sludge rough,the pores increase,and the particle size changes from large to small.The increase of C/N is conducive to the granulation process of sludge.Under the conditions of ultrasonic energy density<0.2 W/m L,irradiation time<20 min and p H 7.9～10,it can promote the secretion of EPS.There are seven denitrifying functional bacteria in the partial denitrification system.Under the condition of p H 11,the partial denitrification functional bacteria Thauera and Hydrogenophaga increase to 1.35%and 4.75%compared with 0.13%and 1.72%of the initial granular sludge.The increase of C/N is conducive to the growth and reproduction of denitrifying bacteria.（2）Study on influencing factors of ANAMMOX.The start-up of anaerobic ammonia oxidation system was completed within 45 days.Under the conditions of influent NO₂^--N and NH₄⁺-N is 30 mg/L,NO₂^--N/Na HCO₃is 1.5,HRT is 4 h and temperature is 35℃,the maximum NH₄⁺-N volumetric load of the system was 0.18kg/（m³?d）,the removal rates of NH₄⁺-N,NO₂^--N and COD were stable at more than90%,98%and 70%respectively,and the effluent NO₃^--N concentration was stable at7.98～8.75 mg/L.After 274 days of continuous culture,the surface of ANAMMOX granular sludge was gradually smooth,and the attachment of new micro aggregates could be observed.The ANAMMOX system contains two kinds of ANAMMOX functional bacteria,namely Candidatus＿Brocadia and Candidatus＿Anammoxoglobus,where Candidatus＿Brocadia is the main functional bacteria,and the highest enrichment proportion can reach 22.97%;Fluorescence quantitative PCR showed that under the condition of stable operation of ANAMMOX reactor,the gene abundance of ANAMMOX functional bacteria could be stable to 9.08 10⁹copies/g VSS.（3）Study on denitrification effect of partial denitrification coupled ANAMMOX process based on homologous sludge.The ANAMMOX reactor was re inoculated with partial denitrification homologous sludge and started up for 33 days.After startup,it was coupled with partial denitrification.The removal rate of NH₄⁺-N in the coupling process was maintained at more than 90%,and the removal rates of COD and NO₃^--N were stable at more than 80%.After domestication,the morphology of homologous sludge is obviously different.There is a layer of hardening material on the surface of partial denitrification granular sludge,which is extruded and bonded by many strip and spherical aggregates to form a particle structure.The anaerobic ammoxidation granular sludge is wrapped by filamentous bacteria,and the surface is fluffy and has many pores.The dominant microbial functional bacteria in homologous sludge will evolve in different directions.In the partial denitrification,the functional bacteria Hydrogenophaga,Thauera and Halomonas are enriched to13.14%,13.10%and 8.47%respectively compared with 0.93%,0.13%and 0%of the initial granular sludge.Halomonas is a unique functional bacteria in the continuous partial denitrification system;In tne ANAMMOX reactor,functional bacteria Candidatus＿Kuenenia、Candidatus＿Anammoxoglobus and Candidatus＿Brocadia increased to 5.50%,0.22%and 0.02%respectively compared with 0%of the initial granular sludge.This study closely follows the technical requirements of sewage biological denitrification,constructs the partial denitrification,ANAMMOX and coupled biological denitrification system based on homologous sludge,and explores the influencing factors and reaction mechanism of partial denitrification and ANAMMOX,so as to provide a theoretical basis for strengthening the feasibility and stability of partial denitrification coupled ANAMMOX process.