Nitrogen removal performance of A/O process with two-sludge system
To address the low utilization efficiency of organic matter by denitrifying bacteria in traditional A/O processes,the complexity of A2N(anaerobic/anoxic-nitrification)process steps,and the high concentration of effluent ammonia nitrogen,a sludge-water separation reactor was proposed.The two-sludge system and A/O process were combined to build the A/O two-sludge process to tackle these challenges.The denitrification performance,variations in microbial communities,and nitrogen transformation patterns during the process operation were studied,the development potential of the sludge-water separation reactor and the A/O two-sludge process based on the research results were evaluated.Additionally,the issues that require optimization in both the process and reactors were summarized and the strategies to address these challenges were raised.The result showed that at an influent nitrogen loading of 0.11 kg·(m3·d)-1,the nitrogen removal load of the process could reach 0.089 kg·(m3·d)-1.The NH4+-N removal efficiency exceeded 95％,COD removal rate surpassed 90％,and TN removal rate exceeded 80％,which could ensure the long-term stable operation of systems.Analysis of the nitrogen transformation patterns indicates that the reaction rate of the denitrification process was the limiting factor in improving the denitrification efficiency of A/O two-sludge process.Increasing the contact time of organic matter in the anoxic tank was crucial for improving the organic matter utilization rates.Therefore,it is necessary to optimize the current carbon source addition method,influent mode,or the number of reactors in the process for further increasing the process efficiency in utilizing carbon sources.The microbial community structure suggests that the cooperative action of denitrifying bacteria,such as Thauera,Nitrospira,Caldilineaceae,along with the predominant heterotrophic nitrification-aerobic denitrification bacterium Paracoccus,was the key factor in maintaining high removal efficiencies of NH4+-N and TN.In conclusion,the A/O two-sludge process had an excellent denitrification performance and a practical application value.The results of this study can provide a reference for subsequent optimization research to address existing deficiencies in both the process and reactors.
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