Optimization Of Autotrophic Nitrogen Removal Process And Effect Of Nano Fe₂O₃ On Anammox

With the deepening of research,the single-stage autotrophic nitrogen removal derived from shortcut nitrification and anammox has been widely concerned for its advantages of no additional carbon source and less sludge production.Due to the complex structure of anaerobic ammonia oxidizing bacteria（AAOB）,ammonia oxidizing bacteria（AOB）and nitrite oxidizing bacteria（NOB）in Single stage autotrophic nitrogen removal process,there ARR still some problems such as slow start-up and unstable operation.In recent years,with the wide use of nanomaterials in consumer and industrial products,the public is concerned about its potential environmental impact.As a completely anaerobic bacteria,AAOB grows slowly,has a long doubling time,is not easy to accumulate,and is prone to instability due to changes in external environment.As an important part of Single stage autotrophic nitrogen removal process,the stable nitrogen removal efficiency of anammox is essential for Single stage autotrophic nitrogen removal system.The influence of nano materials on Anammox process and its impact on the environment have not been generally agreed.It is necessary to find more effective ways to mitigate the adverse effects or make full use of nano materials to enhance the performance of wastewater biological treatment system.In order to solve the above problems,In this paper,sequencing batch reactor（SBR）was used to realize the rapid start-up of shortcut nitrification,and the energy efficiency of anammox system was optimized in upflow anaerobic sludge bed reactor（UASB）.Then,the changes of denitrification performance,functional bacteria activity and microbial community structure before and after energy efficiency optimization of single-stage autotrophic denitrification system were explored,which provided theoretical basis for energy efficiency optimization of single-stage autotrophic nitrogen removal system.Finally,the long-term and short-term effects of nano Fe₂O₃ on Anammox were studied to provide reference for exploring the resistance of anammox to nano materials.The conclusions ARR as follows（1）SBR reactor was used for shortcut nitrification,the influent NH₄⁺-N concentration was 130 mg/L,the p H was maintained at 7.6-7.7,and the DO value was gradually reduced to 0.6-0.7 mg/L.through the residual NH₄⁺-N strategy,the effluent FA was increased to about 0.1-1.0,which successfully promoted the enrichment of AOB and the inhibition of NOB.On the 40th day,the ammonia nitrogen removal rate（ARR）was 80.7%,the nitrite nitrogen accumulation rate（NAR）was more than 80%,and the ammonia nitrogen removal load（ARL）was 1.39 kg N/m³/d.the short cut nitrification was successfully started.In the optimization stage of shortcut nitrification,the concentration of NH₄⁺-N in the influent was 150 mg/L,the average ARR was 80.2%,NAR was stable at about 94.4%,and the maximum value of ARL was 1.52 kg N/m³/d.the short cut nitrification was operated efficiently and stably.（2）In the energy efficiency optimization stage of Anammox,the total nitrogen load was gradually increased by adjusting the flow rate and increasing the influent NH₄⁺-N and NO₂^--N.after 38 days of operation,the total nitrogen removal load（NRL）increased from 0.29 kg N/m³/d to about 0.98 kg N/m³/d.The denitrification performance of anammox was significantly improved.MLSS and MLVSS increased from 6.856 g/L and 4.122 g/L on the first day to 6.947 g/L and 4.485 g/L on the 38th day.（3）The total nitrogen removal rate（NRR）and total NRL of Single stage autotrophic nitrogen removal reactor were increased from 26.51%and 0.14 kg N/m³/d on the first day to 78.48%and 1.20 kg N/m³/d on the 47th day by gradually increasing the influent NH₄⁺-N concentration（80-240 mg/L）in the range of p H 7.8-8.2 and DO in the range of 0.1-0.4 mg/L.The results showed that Candida kuenenia and Candidatus brocadia in aaob increased from 11.10%and 0.02%to 8.97%and 0.12%,respectively;the abundance of Nitrosomonas increased from 0.09%to 0.17%;the abundance of Nitrospira in NOB decreased from 2.16%to 0.11%.（4）When the concentration of nano Fe₂O₃ was 1-10 mg/L,the anammox reaction was not affected in the short experiment;when the nano Fe₂O₃ was 20 mg/L,the anammox rate（SAA）decreased by 0.052 g N/g VSS/d and the ARR decreased by 6.33%,but in the range of 20-50 mg/L,NRR and NRL decreased by 12.11%and 0.13 kgn/m³/d respectively.When Anammox was exposed to 50 mg/L nano Fe₂O₃ for a long time,the denitrification performance of anammox decreased to a certain extent.However,the system did not deteriorate with the increase of inhibition time.Among them,haz decreased by 27.9%,while nir K and nir S did not change significantly.At the same time,the secretion of Extracellular polymers（EPS）increased,protein（PN）and Polysaccharide（PS）increased from 28.91 mg/g MLSS and 33.04 mg/g MLSS to 36.34mg/g MLSS and 37.04 mg/g MLSS respectively.