Enrichment And Nitrogen Removal Of AOA From Wastewater Treatment Plants

Due to the improvement of sewage treatment plant discharge standards,the sewage discharge standards were facing great pressure,especially the discharge of nitrogen,so it was urgent to find a more efficient,more energy saving denitrification process.AOA had the advantages of high ammonia and oxygen affinity as well as lower release of greenhouse gas N₂O.It could more thoroughly remove ammonia and save energy at the same time,which may be of great significance for energy saving and emission reduction of sewage treatment plants.In this paper,through the enrichment of AOA,high-throughput sequencing,PCR,q PCR and other microbial means to analyze the changes in its population structure during the enrichment period.At the same time,the influence of various factors and the addition of NH₂OH on its activity was discussed,and the denitrification pathway and the release of N₂O were analyzed.At last,AOA and Anammox coupling denitrification process was developed,and the contribution of each stage was analyzed.The main conclusions of this paper were as follows:(1)Two kinds of simulated wastewater were used to enrich AOA in the activated sludge of sewage treatment plant.The experimental results showed that the simulated wastewater B was more suitable for AOA enrichment,and the addition of pyruvate might be the main reason for the successful enrichment of AOA.After 600 days of enrichment,AOA of 1.4×10⁷ copies/m L was finally obtained.Through high-throughput sequencing,the enriched AOA was identified as Nitrosocosmicus genus,which was named Nitrosocosmicus DAB1.The abundance accounted for 99.0%of the total archaea,the morphology was 1.2?m spherical archaea with a doubling time of4.5 days,and the activity was 233.9?mol/gprot·d.AOB was not detected in the enriched culture.(2)The p H range of Nitrosocosmicus Da B1was 6.0-8.5,and the optimal p H was 7.5.Nitrosocosmicus Da B1 had the temperature range of 28-40?,and the optimal temperature was 35?.The adhesion of Nitrosocosmicus Da B1 was analyzed by EPS.Nitrosocosmicus Da B1 would synthesize more polysaccharides to maintain its growth and survive in extreme environment at<28?or>40?.Moreover,at the optimal temperature(35?),its enzyme activity was the highest and more transporters were synthesized.The humic acid in EPS had no significant effect on temperature.The semi-saturation constant(K_m)for ammonia and oxygen were 11.0±3.7?M NH₄⁺-N+NH₃(?0.1?M NH₃)and 4.1±2.5?M.The semi-saturation constant(K_m)for ammonia and oxygen were similar to the other known AOA and Comammox,lower than AOB.Nitrosocosmicus Da B1 had the best activity of 56.0?mol N/gprot·d when the concentration of ammonia was 40 m M.When the concentration of ammonia was 80 m M,which was not significantly inhibited.Combined with the SBR process of the wastewater treatment plant,it was speculated that the key factors for AOA enrichment in the SBR process might be long hydraulic retention time,intermittent aeration,low solid-liquid ratio,tolerance to p H and high ammonia.(3)After adding PTIO,AOA activity was inhibited and ammonia was no longer consumed.NH₂OH and N₂O were generated during the oxidation of ammonia by AOA.The maximum accumulation of NH₂OH and N₂O were 6.1?M and 102.8 n M.In the process of ammonia oxidation,the N₂O produced by AOA was only 0.05%(N₂O/NH₄⁺) similar to that of Comammox,but far lower than that of AOB.By calculating its metabolic pathway,it was found that 2.9%NH₄⁺was assimilated and 97.1%was oxidized to NH₂OH during ammonia oxidation of AOA.0.05%was converted to N₂O, and 97.05%was further oxidized to NO,NO₂^-.The metabolic pathway of AOA might be NH₄⁺?NH₂OH?NO?NO₂^-.At the same time,in order to explore the influence of intermediate product NH₂OH on AOA activity,it was found that NH₂OH could be naturally decomposed in the natural environment,and the decomposition rate was very fast.50%NH₂OH was decomposed in 4.5 hours and 120 hours was complete decomposition,during production 107.5?M NO₂^-.When the substrate contains both NH₂OH and NH₄⁺,NH₂OH was preferentially utilized by AOA and AOB,and adding NH₂OH could inhibit the activity of AOA while promote the activity of AOB.When only NH₂OH was used as the substrate,both AOA and AOB could quickly utilize NH₂OH,and AOB utilized NH₂OH faster than AOA,but the release of N₂O was 2.2 times that of AOA.The addition of NH₂OH increased the N₂O release of AOA and AOB.(4)After more than 100 days of Anammox load test,when the reactor was not affected by temperature,the final effluent NH₄⁺and NO₃^-remained at 0.99 m M and 0.9 m M without NO₂^-accumulating.NH₄⁺:NO₂^-:NO₃^-was 1:1.25:0.18 was close to the theoretical value.The removal efficiency of NH₄⁺was higher than 80%and the maximum NH₄⁺loading load was 5.04 m M/d.Meanwhile,it was found that temperature had a great influence on Anammox.The room temperature drops from33°C to 20°C(below 10°C at night),which reduced the NH₄⁺removal efficiency from80%to 20%.When the temperature recoverd from 25?,the Anammox activity could be recovered after 15 days.After AOA coupling with Anammox,NH₄⁺was firstly oxidized by AOA to oxidize 55%NH₄⁺to NO₂^-,and then the resulting NO₂^-and the remaining 45%NH₄⁺were converted to N₂ by Anammox.Finally,the effluent NH₄⁺and NO₃^-remained at 60?M(0.84 mg/L)without NO₂^-.During this period,NH₄⁺:NO₂^-:NO₃^-=1:1.25:0.22 was close to the theoretical value(1:1.32:0.26),and the total nitrogen removal efficiency was higher than 80%.Through high-throughput sequencing analysis,it was found that the abundance of Anammox population increased by 44.1%after accessing to AOA effluent.Ca.Kuenenia(30.6%)was the dominant population,the abundance of denitrifying bacteria decreased by 22.8%,and Pseudomonas was the dominant bacteria(1.2%).The population structure of Anammox was optimized,and Anammox gradually became the dominant bacteria.Meanwhile,the nitrogen removal contribution of Anammox was improved.The contribution ratio of Anammox to denitrification was 88.3%and 11.7%by isotope tracer method.Under the combined action of AOA,Anammox and denitrifying bacteria,the combined process could guarantee the stable and efficient denitrification of low ammonia wastewater,and the total nitrogen removal efficiency was maintained at 86.7%,indicating that the combined process had high efficiency,feasibility and stability.Comprehensive,AOA equipped higher affinity to ammonia and oxygen than AOB and released lower N₂O.Long hydraulic retention time,intermittent aeration,low solid-liquid ratio,tolerance to p H and high ammonia might be conducive to the enrichment of AOA in sewage treatment plants.The development of the combined process of AOA and Anammox provided theoretical guidance for the treatment of domestic wastewater with low ammonium concentration in the future.