| The increase of greenhouse gas(such as CO2,CH4,N2O,etc.)emissions is an important cause of global warming,among which N2O is an significant greenhouse gas.The global warming potential of N2O is about 265 times that of CO2,and it could stablize in the atmosphere for 114 years.The biological nitrogen removal(BNR)process in wastewater biochemical treatment process is an important source of N2O,and its annual N2O emission accounts for about 2.5-25%of the total N2O emission in the world.Investigating N2O emission pattern and generation mechanism in the BNR process for municipal wastewater treatment has great theoretical and practical significance for the reduction of N2O emission.Two wastewater treatment plants(WWTPs)in Jilin area were selected to conduct a field study of the spatiotemporal emission pattern of N2O and the relationship between N2O emission and process type,operating status,water quality parameters,environmental factors and microbial community structure.Based on this,combined with the monitoring data of the WWTP,the lab-scale A/O reactors were used to investivate the process performance and N2O emission under different DO concentrations and pH condition.The microbial community structure under different operating conditions were also analyzed based on the 16S rDNA high-throughput sequencing.It was found that the rapid change of DO level caused the immediate increase of N2O emission rate.The total average gaseous N2O emission under the aeration rates of 0.5,1.0,1.5 and 3.5L/min accounted for 0.011%,0.046%,0.308%and 0.229%of the influent nitrogen.When the DO concentration was 1.67 mg/L,the microbial diversity was higher,and the relative abundances(RA)of denitrifying bacteria and nitrite oxidizing bacteria(NOB)were higher,while that of the detected ammonia oxidizing bacteria(AOB)was the lowest.The network diagram showed that most of the potential denitrifying bacteria were negatively correlated with N2O emissions and positively correlated with AOB,indicating that the regulation and control of denitrifying bacteria,AOB and NOB could be realized by controlling appropriate DO concentration,which could be a feasible strategy to reduce N2O emission.At the influent pH of 5,6,8,and 9(5 days monitoring),the average N2O emissions accounted for 0.329%,0.103%,0.085%,and 0.793%of the total nitrogen in the influent,respectively.The oxic tank was the main source of N2O emission.At the influent pH of 5,the inhibition difference between hydroxylamine dehydrogenase(HAO)and ammonia monooxygenase(AMO)and the chemical reaction between NH2OH and HNO2 were the main reasons for N2O generation,while the influent pH was 9,the incomplete oxidation of NH2OH was the main reason for the generation of N2O.Controlling the pH range of the influent to 7-8 contributed to more efficient denitrification and reduction of N2O emissions.The analysis of microbial community structure showed that there was no significant correlation between N2O emission and nitrifying bacteria and denitrifying bacteria,which indicated that the influence of pH on N2O generation was more likely to be related to the activity of bacterial enzymes and the forms of nitrogenous compounds,but has little to do with the change of bacterial community structure itself.Therefore,adjusting and controlling the pH within a certain range can reduce the emission of N2O in the BNR process. |
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