Application Research Of Nitrogen And Phosphorus Removal Technology Via MBR In WWTP

To address the problem that it is difficult to stably reach the standard for the municipal wastewater treated by traditional biological removal process of nitrogen and phosphorus,this paper,on the basis of systemic analysis for the water quantity of service area and water quality of inflow,focused on facilitating the water outlet from second phase project of a sewage treatment plant in Nanjin to steadily comply to the first level A criteria specified.Herein,this paper proposed an urban sewage treatment process scheme with Anaerobic-anoxic-aerobic-membrane bioreactor（A²/O-MBR）as the core,determined the design parameters of MBR biological reaction tank,demonstrated the main equipment forms and hydraulic flow,and explored the effect of nitrogen and phosphorus removal process via membrane bioreactor on urban sewage treatment and its economic and social environmental benefits,which provided a theoretical and practical basis for the reconstruction and upgrading of municipal wastewater treatment facilities in China.The paper applied the comprehensive water consumption index method per unit population and the average water consumption index method per unit acre to determine the sewage discharge in the service area of the near term（2020）and the long term（2030）,which are 45,000 m³/d and 180,000 m³/d,respectively.On the basis of the statistical analysis for the characteristics of the water quality of the first phase project,the systematic analysis of the water quality of the sewage in the service area of the second phase project was carried out by combining the index analysis with the regional pollution source assessment.The results demonstrated that the main pollutant contents are as follows:SS=180 mg/L,BOD₅=150 mg/L,COD_cr=320 mg/L,TN=38mg/L,NH₃-N=30 mg/L,TP≤5mg/L.Based on the investigation results of regional sewage discharge characteristics,the water quality index evaluation method was furthermore employed to inquire the characteristics of regional wastewater treatment.The results of BOD₅/COD_cr=0.47indicated that the biodegradable organic matter content in sewage was relatively higher.The results of BOD₅/TN=3.97 implied the sufficient carbon source and moderate suspended solid content in the water,which is suitable for biological denitrification.Besides,the results of BOD₅/TP=50 signified that biological phosphorus removal requirements were suitable.Therefore,this study determined the sewage treatment process with A²/O-MBR as the core through the comparison of process schemes.By evaluating the influence of primary parameters on the treatment system,it was determined that the mixed liquor was used in the A²/O-MBR process could be operated in the mode of step-by-step backflow.And the effective inhibition of membrane pollution was realized by aeration flushing,intermittent operation combined with online chemical cleaning and offline restorative cleaning,future confirming the average net water production flux of membrane to be 20 L/（m²·h）.On basis of the analytical results of key factors of MBR process,the hydraulic residence time of biochemical stage,sludge load,sludge age and actual average net water production flux of the membrane was calculated to be 10.07 h,0.065 kg BOD₅/kg MLSS·d,16.33 d,and 19.97 L/（m²·h）,respectively.In addition,on the basis of long-term monitoring for the quality of raw wastewater and treated water of the treatment project,the performance of the membrane bioreactor was investigated in the treatment of urban sewage.The results of the average removal rate of all kinds of pollutants by MBR process were shown as follows:COD_cr:90.00%;BOD₅:94.47%;SS:95.88%;TN:70.61%;NH₄⁺-N:99.00%;TP:94.22%.The main pollutant content in the water treated was:COD_cr=15.90 mg/L;BOD₅=3.14 mg/L;SS=4.52 mg/L;TN=5.23 mg/L;NH₄⁺-N=0.09 mg/L.The effluent water quality was stable and reached the 1A permitted criteria of"Discharge standard of pollutants for municipal wastewater treatment plant"（GB 18918-2002）.The application of membrane bioreactor for nitrogen and phosphorus removal technology in a sewage treatment project has realized the effective treatment of regional sewage in Nanjing,and the annual average emissions of carbon,nitrogen and phosphorus pollutants were reduced by 2,274.63 tons,190.58 tons and 22.86 tons,respectively.Therefore,these results of the study were of great significance to strengthen regional pollution control and improve regional water environment quality.