Study On Nitrogen Removal Efficiency Of Partial Denitrification Anaerobic Ammonia Oxidation Process Based On IFAS System

As a new biological nitrogen removal process with great research and potential engineering application value,partial denitrification anaerobic ammonia oxidation process has become one of the hot research topics in the field of sewage biological nitrogen removal,which has attracted the attention of many scholars.Firstly,this paper realizes the rapid set-up of PD/A-IFAS process,and studys the operation characteristics of the process driven by macromolecular carbon;subsequently,An HA-PD/A process is used to realize the synchronous and efficient treatment of carbon and nitrogen pollutants in domestic sewage and nitrate wastewater;lastly the operation characteristics of the coupling process under the impact of nitrogen load are studied,which provides a new idea for the efficient treatment of low carbon ratio wastewater in the future.Specific conclusions are as follows（1）In order to quickly start the high-efficiency PD/A process based on IFAS system and explore the operation characteristics of the process under different carbon source conditions,glucose and new combined packing were added into Anammox-CSTR to quickly start PD/A-IFAS process,The operation characteristics of PD/A process driven by different carbon source conditions（glucose;mixture of glucose and starch）and different COD/NO₃^--N（2.0,3.0,4.0,5.0,4.5;4.5,5.0,5.5）were studied,and the distribution of microbial community in corresponding stages was compared and analyzed.The results showed that with glucose as the only carbon source and COD/NO₃^--N of 4.5,the efficient PD/A-IFAS process was successfully set up on the 90th day,and the corresponding TN removal rate was 93.89%.At this time,PD-Anammox process,as an absolutely dominant nitrogen removal path in the system,contributed 95.83%of TN removal,the contribution rate of the corresponding denitrification process to TN removal was only 4.17%.Under the driving of mixed carbon source,the TN removal rate of PD/A system decreased to 90.53%,at this time,COD/NO₃^--N increased to 5.0,and the contribution rate of denitrification process to TN removal increased to 8.48%.During the test,IFAS system showed good sludge interception capacity and matrix transfer efficiency.The batch test results showed that the effective utilization rate of mixed carbon source of starch and glucose by PD bacteria was insufficient,which greatly restricted the efficient removal of nitrogen.Microbial high-throughput sequencing showed that Proteobacteria,as the absolute dominant bacteria in PD/A system,had a relative abundance of more than 50%in S1（single carbon source）and S2（mixed carbon source）;Candidatus Brocadia and Thauera with a certain abundance were the key to the efficient synergistic denitrification of PD/A system.The relative abundances of the two functional bacteria in S2 were 2.97%and 6.52%respectively,slightly lower than 3.41%and 6.94%in S1;In addition,the low relative abundance of anaerobic hydrolytic acidification（An HA）was the main reason for the decline of mixed carbon source utilization in S2.（2）Based on the research results of the last stage,the front anaerobic hydrolytic acidification（An HA）process was introduced to construct an efficient An HA-PD/A coupling nitrogen and carbon removal system,which realized the synchronous and efficient treatment of low carbon nitrogen ratio simulated domestic sewage and low concentration nitrate simulated wastewater.By controlling the influent NO₃^--N/NH₄⁺-N=1.2、COD/TN=2.36,the subsection influent ratio of domestic sewage to 3:7 and the An HA reactor HRT=3.2 h,the An HA-PD/A system successfully removed 94.78%of nitrogen in sewage,and the corresponding effluent TN concentration was only 5.47 mg·L^-1,which was far lower than the class a discharge standard of urban sewage treatment plants in China.During stable operation,PD-Anammox process was the most important nitrogen removal process in An HA-PD/A system,and its contribution rate to TN removal was as high as 95.87%.The results of gas chromatography showed that acetic acid,as the main organic component of An HA effluent（43.65%）,that is,optimizing the organic composition of domestic sewage can effectively promote the supply process of NO₂^--N in PD/A system.Microbial high-throughput sequencing showed that commonas and omatilinea,as the hydrolysis and acidification bacteria with the highest relative abundance in An HA system,played an important role in the degradation and acid production of macromolecular organics,with corresponding abundances of 2.97%and 3.74%respectively;The main dominant functional bacteria in PD/A system were Candidatus Brocadia and Thauera,with corresponding abundances of 2.93%and 7.37%respectively.Finally,based on the conclusions of this study,a potential engineering application scheme was proposed to realize efficient sewage treatment and sludge resource utilization.（3）In order to study the operation characteristics of An HA-PD/A process under the impact of nitrogen load,shortened the HRT of PD/A-CSTR reactor,and increased the nitrogen load of system inlet water from 0.44 kg N/m³.d to 0.616、0.792 and 1.1kg N/m³.d.The changes of nitrogen removal performance of the coupling system were analyzed,its activity and specific activity were characterized by ectopic batch test,and the distribution of microbial community under different nitrogen load were compared.The results showed that under the impact of nitrogen load,the denitrification performance of the coupling system decreased sharply（94.63%,90.13%,85.17%and 74.35%）,and the denitrification contribution showed an upward trend（4.76%,8.93%,25.87%and 76.51%）.The batch test results showed that the nitrogen load impact strengthened the denitrifying nitrogen metabolism pathway in the system,resulting in the serious decrease of the coupling nitrogen removal performance of the system.Microbial high-throughput sequencing showed that under the impact of nitrogen load,the relative abundance of the main synergistic denitrification functional bacteria（Thauera and Candidatus Brocadia）in the coupling system decreased significantly from 8.42%and 3.07%to 4.79%and 1.78%respectively,while the relative abundance of denitrifying bacteria such as denitratima increased from 4.57%to 7.39%.