| N2O is an important greenhouse gas in the atmosphere and its greenhouse effect is approximately310times as much as CO2. Additionally, N2O is the main reason to cause ozone depletion, and the presence of it in the atmosphere can also form acid rain. It has been reported that the biological nitrogen removal process of sewage treatment is one of the main sources of N2O. Therefore, it has a positive significance to study the N2O generating mechanism in the biological wastewater treatment process and to propose the feasible and effective control strategy of N2O reduction.Focused on the anoxic-oxic SBR biological nitrogen removal system and based on the previous research on the N2O generating mechanism in the biological wastewater treatment process, four feasible N2O reduction strategies were proposed in our study, including add denitrifying sludge, add nitrifying bacteria, add external carbon source and step-feed. Furthermore, the pollutant removal and N2O reduction effects of the proposed strategies were evaluated, and then the practical reduction strategy was determined. Meanwhile, under the different reduction strategies, the molecular biotechnology was used to analysis the changes of the microbial community structure and the number of microbial community which associated with N2O emissions, to verify the regulation of reduction strategies on the microbial community structure and to explain the effect of the strategies on microbial community structure by means of combining with the correlation.The results indicate that removal effects of COD, ammonia nitrogen and total phosphorus were pretty good under the four strategies of N2O reduction and the effect of different strategies on pollutant removal was not apparent. However, there was a distinct difference in the total nitrogen’s removal efficiency, external carbon addition and add denitrifying sludge had a better effect on total nitrogen remove, achieving76.45%and68.69%, respectively. In the systems of adding denitrifying sludge and employing step-feed reduction strategy, the emission of N2O were reduced by25.21%and28.82%, N2O-N conversation rate decreased by39.78%and46.24%, respectively. And the emission of N2O in the external carbon source system increased by6.97%, however, the total nitrogen’s removal efficiency was quite good with the N2O-N conversation rate decreased by16.2%. In addition, by adding nitrifying bacteria, the emission of N2O and N2O-N conversation rate increased by13.80%and5.38%, respectively. Consequently, adding denitrifying sludge, adding external carbon source and adopting step-feed are feasible N2O reduction strategies.In a typical cycle, N2O emissions are mainly generated in the aerobic stage under different N2O reduction control strategies while it was not evident in anoxic stage. In the aerobic stage, N2O emission rate and the concentration of NO2-has a significantly positive correlation, indicating the source of N2O in the aerobic stage is denitrification. The changes of microbial community structure under different reduction strategy were analyzed by using the molecular biotechnology and employing the functional genes amoA and nosZ for molecular markers. The results show that the community structure of denitrifying bacteria in the various systems had no significant change and only slight changes happened in abundance of microbial community. The increase in diversity and abundance of ammonia-oxidizing bacteria were observed after adding nitrifying bacteria, and then the Nitrosomonas were enriched. External carbon source strategy reduced the ammonia oxidizing bacteria community structure and diversity and the dominant bacteria of the Nitrosomonas were enriched largely. Employing step-feed technique and adding denitrifying sludge had little effect to ammonia oxidizing bacteria community structure. According to the comprehensive analysis of microbial community structure changes and differences in N2O emissions, the changes in microbial community structure have great influence on N2O generation. The increase in the diversity and abundance of nitrifying bacteria will lead to a significant increase in N2O generation and conversion rate. On the contrary, increasing the proportion of denitrifying bacteria will result in reduction in N2O emissions reduction. Regulating and controlling the microbial community structure plays an important role in the reduction of N2O. |
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