Characteristics And Mechnasims Of Nitrogen Removal Of Aerobic Denitrifier Pseudomona Stutzeri T13

Aerobic denitrifying biological denitrification technology has always been one of the hotspots in the field of biological denitrification technology research and development due to its unique advantages such as saving construction investment,reducing operational costs,and realizing synchronous carbon and nitrogen removal.However,in the research of aerobic denitrification direction,there are still some scientific problems to be solved,such as how to promote the denitrification performance of aerobic denitrification bacteria and how to deeply reveal the action mechanism of aerobic denitrification.Based on this,this study took the isolated aerobic denitrification strain T13 as the research object and carried out research about promoting the growth and denitrification performance of the strain T13,as well as in-depth analysis of the action mechanism of aerobic denitrification.Aiming at how to improve the growth rate and denitrification performance of aerobic denitrifying bacteria,it is considered that appropriate addition of some metal ions can promote the metabolic activity of microorganisms.Therefore,the denitrification performance of strain T13 was first optimized,and the influences of carbon source,C/N,temperature and p H on denitrification performance of strain T13were investigated,respectively.The results showed that the strain T13 had strong environmental adaptability,and the optimal culture condition was sodium succinate as carbon source,C/N at 8,temperature at 30?,and p H at 8.The effect of metal ions on the denitrification performance of strain T13 was studied under the optimal culture conditions.The results showed that Fe³⁺ions could promote the growth and aerobic denitrification performance of strain T13.When the concentration of Fe³⁺ions increased from 0.004 mmol/L to 0.036 mmol/L,the growth rate of strain T13increased from 10.35 mg Biomass-N L^-1 h^-1 to 13.30 mg Biomass-N L^-1 h^-1 with an increase of 28.5%,and the reduction rate of NO₃^--N increased from 5.25 mg L^-1 h^-1to 19.65 mg L^-1 h^-1 with an increase of 2.74 times.The gaseous end product of aerobic denitrification of strain T13 was N₂(>99%),and the accumulation of NO and N₂O in aerobic denitrification was very low.Compared with the control group(0 mmol/L Fe³⁺),0.036 mmol/L Fe³⁺resulted in the increased relative expressions of key functional genes for denitrification such as nap A,nir S,nor B and nos Z by 3.21,8.17,1.82 and 7.95 times,respectively,and activities of nitrate reductase and nitrite reductase increased by 4.2 and 13.5 times.In view of the unclear stoichiometric relationship of aerobic denitrification,the stoichiometric characteristics of strain T13 were studied.The results showed that the empirical molecular formula of strain T13 cell was C_4.98H_6.98O_1.98N,which was close to that of traditional heterotrophic microorganism cells(C₅H₇O₂N).The stoichiometric parameters of strain T13 were obtained under different nitrogen source conditions,and the electron distribution proportion of strain T13 was clarified under different nitrogen source conditions.For example,the stoichiometric parameter f_s of strain T13 was 0.538 when NH₄⁺-N and NO₃^--N coexsited,indicating that 53.8%of the organic matter consumed by strain T13 was used as carbon source for the synthesis of cellular material,and the remaining 46.2%as electron donor was transferred to the electron acceptor for generating energy.Among them,44.2%of the electrons transferred to the electron acceptor were transferred to nitrate,and 55.8%were transferred to O₂.The stoichiometric parameter f_s of strain T13 was higher than that of traditional anoxic denitrifying bacteria,but lower than that of f_s^o estimated by energetics.Experimental results of dynamic characteristics showed that the relationship between the specific growth rate of strain T13 and the concentration of COD,ammonia nitrogen,and nitrate can be described by the multimatrix Monod equation(R²>0.95).Among them,the half-saturation constant of COD(K_COD),ammonia nitrogen(K_NH4),nitrate(K_NO3)were 125.07,6.95,and 2.72 mg/L,respectively,in strain T13.The relationship between the specific growth rate of strain T13 and nitrite concentration can be described by the inhibitory Monod equation(R²>0.95).Among them,the half-saturation constant of nitrite(K_NO2)and the half-saturation inhibition constant(K_{i NO2})were 18.34 and 209.07 mg/L.The growth and denitrification performance of strain T13 under different conditions were numerically simulated by AQUASIM software using the“two-step denitrifying”model based on the obtained stoichiometric parameters(including kinetics constants)of strain T13.The results showed that the obtained stoichiometric parameters can well describe the growth and aerobic denitrification performance of strain T13,with R² higher than0.95.Aiming at the problem that the mechnasim of effec of DO on aerobic denitrification is still unclear,the influence and mechanism of DO on the aerobic denitrification of strain T13 were studied using the Membrane aerated biolfilm reactor(MABR)with its characteristics of bubble-less aeration and flux analysis.The results showed that the average DO concentration increased from 0.02 to 4.23 mg/L and the average removal efficiency of NH₄⁺-N and COD increased.However,the average removal efficiency of nitrate decreased,and the accumulation amount of nitrite increased with the gradual increase of O₂ inlet pressure from 2 psig to 10 psig.Flux analysis showed that when O₂ pressure was 2 psig,the actual electron flux consumed by O₂ was 5.60 e^-equivalent m^-2 d^-1,which was basically equivalent to the theoretical maximum O₂ transfer flux(5.80 e^-equivalent m^-2 d^-1)under this condition,and O₂supply was relatively insufficient.When O₂ inlet pressure was 10 psig,the actual electron flux consumed by O₂ was 14.65 e^-equivalent m^-2 d^-1,less than the theoretical maximum O₂ transfer flux(23.2 e^-equivalent m^-2 d^-1)under this condition,and O₂was sufficiently supplied.Expression of nap A and nor B gene were less affected by the change of DO concentration,with the highest relative expressions at DO concentration of 0.92 and 0.19 mg/L,respectively,which was 2.15 and 1.85,respectively,while nir S and nos Z gene were more affected by the change of DO concentration,with the highest relative expressions at DO concentration of 0.19 mg/L,which was 6.50 and 6.13,respectively.