Study On Start-up Process And Microbial Ecological Characteristics Of Simultaneous Nitritation,Anammox And Denitrification Process

The discharge of nitrogen-containing wastewater has a great impact on the environment,which is easy to cause water eutrophication,and has become an environmental problem of great concern.Simultaneous nitritation,anammox and denitrification（SNAD）process can exhibit a good performance for nitrogen and carbon removals.However,its related research was mainly focused on the high ammonia nitrogen wastewater treatment and limited research was demonstrated regarding on this process for the low ammonia and low C/N ratio wastewater treatment.In view of this,this thesis firstly enhanced the anammox process,and studied the physicochemical properties and nitrogen removal performance of anammox granular sludge with different particle sizes.Then,the SNAD process was started up with investigating the nitrogen removal performance,microbial activity and sludge properties during the start-up process.In addition,metagenomics analysis of microbial community was demonstrated during the startup in order to provide theoretical guidance for the application of SNAD for low ammonin and low C/N ratio wastewater treatment.The main conclusions are as follows:（1）By inoculating anammox granular sludge,the anammox process was successfully started up within 29 days by shortening the hydraulic retention time（HRT）.Finally,NRE reached 80.85±0.81%,and?NO₂^--N/?NH₄⁺-N ratio remained around1.32.Granular sludge with particle size of 1.5-2.0 mm increased with accounting for25.68%.3D-EEM analysis results showed that the fluorescence intensity of protein increased continuously during startup,and FT-IR analysis results also indicated that amino acid played an important role in the anammox sludge granulation.（2）The analysis results of physicochemical properties of anammox granular sludge with different particle sizes showed that porosity,wet density and TB-EPS were positively correlated with the particle size,whereas moisture content,SMP and LB-EPS were negatively correlated with the particle size.3D-EEM results showed that tryptophan played an important role in granular growth.Granular sludge with 2.0-2.5mm showed the highest integrity coefficient,and PN/PS reached the highest in TB-EPS.3D-EEM results further showed that its tryptophan content was the highest,so that its physicochemical properties was relatively stable.In adddition,the anammox activity was the highest when the particle size was 2.0-2.5 mm.Combined with the analysis of physicochemical properties and biological performance,Anammox granular sludge with particle size in the range of 2.0～2.5 mm should be taken as the target of orientational acclimation and cultivation.（3）Based on the start-up of Anammox process,the CANON process was started up by controlling the aeration frequency,and finally achieved an ammonia removal efficiency（ARE）of 98.27%.Afterwards,organic carbon source（sodium acetate）was introduced into the process and the C/N ratio was controlled at 0.5,and nitrogen removal efficiency（NRE）and the chemical oxygen demand（COD）removal efficiency（CRE）reached around 90.25%and 85.22%,respectively,and the synergy of Aer AOB,An AOB and DNB was realized for the nitrogen and carbon removals to achieve a successful start-up of the SNAD process.The synergistic nitrogen and carbon removal of Aer AOB,An AOB and DNB was realized.The particle size increased gradually with the process,which was related to the increased secretion of EPS and SMP.The activity increased continuously and the stability of particles increased.3D-EEM showed that tryptophan was closely related to particle size growth during SNAD process.（4）Through metagenomics analysis,Nitrosomonas,the dominant bacteria of Aer AOB,decreased first and then increased,and were enriched in CANON process.At the initial start-up,Candidatus＿Kuenenia was the dominant bacterium,while at the successful start-up of SNAD process,Candidatus＿Brocadia became the dominant bacterium of An AOB.Denitrifying bacteria could cooperate with Aer AOB and An AOB to remove nitrogen actively.The expression of hao and amo genes related to Aer AOB increased in CANON process,indicating the enrichment of Aer AOB.Similarly,the An AOB related genes hzs and hdh decreased first and then increased,indicating that An AOB gradually adapted to the environment with low DO concentration and C/N ratio.The abundance of denitrifying related genes（nar G,nar H,nir S,nir K）was high,which could improve the total nitrogen removal efficiency in the system to a certain extent.The predicted nitrogen metabolism pathway showed that in SNAD system,the synergism of nitritation,anammox and denitrification could be achieved to enhance nitrogen and carbon removals.