Nitrogen Removal Performance And Microbial Structure Analysis Of Partial Nitritation-Anammox Process For Iron And Steel Processing Wastewater

Iron and steel processing wastewater had the characteristics of high ammonia nitrogen and low organic matter concentration.It was suitable for partial nitrification-anaerobic ammonia oxidation process（PN-A）,but it was seldom studied and applied in practice.It studied the start-up control and stable operation of one-stage PN-A process to treat simulated steel processing wastewater,and discussed the feasibility of this process to treat real steel processing wastewater.By using sequencing batch activated sludge reactors and sequencing batch biofilm reactors filled with spiral fibers,the start-up of partial nitrification was studied.The results showed that,compared with activated sludge systems,dissolved oxygen（DO）in biofilm system was less affected by changes in aeration rate,the ratio of nitrite nitrogen（NO₂^--N）to ammonia nitrogen（NH₄⁺-N）in effluent was stable at 1.2:1 to 1.7:1,and the activity of ammonia oxidizing bacteria（AOB）was stable and can adapt to higher DO levels.Biofilm system was more suitable as a partial nitrification pretreatment process for ANAMMOX.PN-A process was successfully started in a sequencing batch biofilm reactor using helical fiber as carrier in 105 d with high DO(3.0±0.5 mg·L^-1).High-throughput sequencing analysis showed that Nitrosomonas（AOB）and Candidatus＿Kuenenia（AMX）were the main nitrogen removal functional bacteria.At 30℃～23℃,the average removal rates of NH₄⁺-N and total nitrogen（TN）were93.61%and 76.94%,respectively.At 23℃～20℃,the activities of AOB,NOB and AMX were inhibited,the ammonia oxidation rate（AOR）decreased from 11.20mg·L^-1·h^-1 to 2.33 mg·L^-1·h^-1,the total nitrogen removal rate（NRR）decreased from13.37 mg·L^-1·h^-1 to 3.02 mg·L^-1·h^-1,and the average removal rates of NH₄⁺-N and TN decreased to 18.29%and 15.20%,respectively.After the temperature decreased,the relative abundance of Candidatus＿Kuenenia increased from 5.09%to 21.21%,after the temperature raised to 28℃,the relative abundance decreased to 9.21%,the relative abundance of Nitrosomonas increased from 2.79%to 9.46%,and the total nitrogen removal rate of the system recovered as 80%.It could be seen that although the low temperature environment inhibited the activity of Candidatus＿Kuenenia,it enhanced its enrichment and proliferation ability,and Nitrosomonas was more suitable for survival in higher temperature environment.The experimental results of PN-A process treating real iron and steel processing wastewater showed that TN removal rate was maintained at 60%to 80%in stable operation stage.As time went on,effluent NO₃^--N accumulated in large quantities,and overall denitrification performance deteriorated.The abundance of Candidatus＿Kuenenia decreased from 9.21%to 6.32%during simulated wastewater treatment stage,while the abundance of Nitrosomonas remained at 8%to 9%,and the abundance of NOB bacterium unidentified＿Nitrospiraceae increased from0.02%to 1.88%during simulated wastewater treatment stage.at this time,the effluent NO₃^--N reached 40 mg·L^-1,and the nitrogen removal performance worsened.