Study On Strengthen Denitrification Of A~2/O Based On Partial Nitrification Coupled With Anammox System

In recent years,the increasingly strict discharge standards of the urban sewage have made people pay more and more attention to the intensified removal of nitrogen pollutants in wastewater.However,the lack of carbon sources from water inflow is the main obstacle for most sewage treatment plants to improve the efficiency of nitrogen removal.Thus,on the basis of partial nitrification and anaerobic ammonia oxidation process can save carbon source scientific theory,the traditional A²O system was selected as the study object in the paper,through adjusting the proportion of aeration partition,dissolved oxygen?DO?concentration and sludge renttention time?SRT?to build the shortcut nitrification coupled anaerobic ammonia oxidation?PNA?system,which provided the scientific basis for the sewage plants' upgrading.The carbon nitrogen ratio of wastewater is 5?COD=248 mg/L,TN=54 mg/L,NH₄⁺-N=52 mg/L?and under the condition of continuous and stable operation of the system for 140 d,in the process of the experiment,the system effluent of COD concentration around30 mg/L,the concentration of NH₄⁺-N and TN also can meet the standard of level of stair A.the system in the V_anaerobic:V_aerobic=4:4,dissolved oxygen?DO?was 0.3?0.7 mg/L,when the sludge renttention time?SRT?of 15 d nitrogen removal efficiency under the condition of the best,The average concentration of NH₄⁺-N and TN in the effluent was 1.20 mg/L and 7.03mg/L,respectively.In order to further strengthen the denitrification performance and promote the formation of anaerobic ammonia oxidation,adding the packing material to the anoxic zone and providing attched the carrier,and further reduce the carbon nitrogen ratio of water?5?1?to study the system demand for carbon source,the results showed that the effluent to the anoxic zone after adding the filler system average concentrations of NH₄⁺-N and TN were further down to 0.52 mg/L and 5.31 mg/L,control system when the system fill carbon nitrogen ratio is 2,it still has the good performance of denitrification,NH₄⁺-N and TN in produced water at this time the average concentration of 4.51 mg/L and 9.38 mg/L,Thus,adding biological fillers to the anoxic zone of the PNA system can further enhance the system's denitrification performance and reduce its demand for carbon sources.In this study,Illumina MiSeq sequencing method was used to analyze the changes of bacterial population in the system.The results showed that by increasing the proportion of anoxic zone in the system and reducing the dissolved oxygen and sludge retention time in the aerobic zone,ammonia oxidizing bacteria?AOB?,nitrite oxidizing bacteria?NOB?and anaerobic ammonia oxidizing bacteria?AnAOB?could be screened to a certain extent.The relative abundance of AOB and NOB at the genus level decreased by 0.8%and 2.4%from the stage?1?4?,and the relative abundance of AnAOB at the genus level increased by 0.27%.The relative abundance of AnAOB at the genus level was increased by 0.07%by adding biological fillers into the anoxic zone,and it was further increased by 0.025%by reducing the influent C/N ratio to 1.Generally speaking,during the construction of PNA system,the co-culture stage of AOB and NOB,the screening stage of AOB and the enrichment stage of AnAOB were experienced.The nitrogen removal pathway of the system was also transformed from the initial nitrification and denitrification to the partial nitrification coupled anammox denitrification.On this basis,adding biological fillers to the system anoxic zone and lowering the low carbon-nitrogen ratio of water intake will further enhance the degree of anammox.