Material Balance Of C,N And P And DNRA In A~2/O Process Of Municipal Wastewater Treatment Plant

Through the material balance of operation unit in the nitrogen and phosphorus removal system of the municipal sewage treatment plant,the reaction route and degree can be analyzed.The problems in the operation of wastewater biological treatment system are solved by material balance.An effective method is provided to save energy and reduce consumption.In addition,for biological nitrogen and phosphorus removal systems,material balance can provide evidence for operation and optimization.Taking A²/O process of a sewage treatment plant in Xi'an as the research object,material balance is calculated for C,N and P,and transformation pathway is analyzed.In addition to NO₃^--N is reduced to N₂ by denitrification,it may also be converted to NH₄⁺-N by DNRA in the biological treatment system of wastewater.The N component of the anaerobic tank influent and effluent water is determined.The whereabouts of N are analyzed by material balance.On this basis,taking sludge of A²/O system as inoculated sludge,the effects of different COD/NO₃^--N on the DNRA process are studied to determine the optimal COD/NO₃^--N ratio in the laboratory stage.Finally,the activated sludge was enriched and cultured under continuous COD/NO₃^--N ratio.The DNRA phenomenon is discussed and causes are analyzed by using 16SRNA and nrfA functional gene sequencing methods in the biological nitrogen and phosphorus removal system of urban sewage.The main conclusions are as follows:?1?Through the material balance of the A²/O process,the results show that there is obvious denitrification in the secondary settling tank.TN removal rate accounts for 24.8%in the secondary settling tank.It shows that the secondary sedimentation tank plays an important role in nitrogen removal while separating muddy water.The anaerobic tank also has denitrification while absorbing organic matter and releasing phosphorus,and the total nitrogen removal rate is as high as 7.7%.In addition,Measurement result display that the average daily loss of TN is177.6 kg and NO₃^--N is 235.2 kg in a 6500 m³ anaerobic tank.The loss of TN is significantly lower thanNO₃^--N,indicating that there may be a conversion process of NO₃^--N to NH₄⁺-N?DNRA process?.?2?Through the DNRA verification experiment,the results show that the DNRA rate increases from 0.5 mg NH₄⁺-N/g?VSS?h to 2.1 mgNH₄⁺-N/g?VSS?h with the increase of COD/NO₃^--N ratio.The presence of DNRA has been demonstrated in anaerobic ponds of municipal wastewater treatment plants.The ratio of nitrate between denitrification and DNRA is the largest in COD/NO₃^--N=10 and the maximum value is 4:1.The best COD/NO₃^--N is 10of DNRA enrichment culture.In addition,The maximum production of NH₄⁺-N increased from2.25 mg·L^-1 to 2.95 mg·L^-1 with increasing temperature at the same COD/NO₃^--N ratio.The optimal temperature is 35°C for enrichment culture of DNRA.?3?The activated sludge was continuously enriched for 50 days under the condition of influent NO₃^--N concentration of 20 mg·L^-1 and COD concentration of 200 mg·L^-1.The effluent NH₄⁺-N concentration reached 10 mg·L^-1,The DNRA process is existed in the biological nitrogen and phosphorus removal system of urban sewage.The main genus of DNRA is Thauera,Hydrogenophaga and Geobacter in the Proteobacteria by 16SRNA and nrfA functional gene sequencing.