Operation Optimization Of A~2/O-MBR Combined Process And Depth Control Of Nitrogen And Phosphorus Removal

In recent years,with the rapid development of China's economy and society,the discharge of urban sewage in various regions has increased sharply,and the problem of water pollution has become increasingly serious,which has seriously restricted the sound and rapid development of China's economy.Excessive levels of nitrogen and phosphorus are the main factors leading to this problem.In order to curb the deteriorating trend of the water environment and maintain the ecological balance of the water environment,China's sewage discharge standards have been continuously improved.For example,the local standards introduced by Tianjin require urban sewage treatment plants(DB12/599-2015)with a design scale of>10000 m3/d.The effluent TN ? 10 mg/L and TP?0.3 mg/L,and it is difficult to achieve this emission standard only through optimization of biological treatment.In order to meet this standard,subsequent chemical phosphorus removal and denitrification denitrification are generally performed after secondary biological treatment.Through orthogonal test,the optimal parameters of the A2/0-MBR combined process during stable operation were determined,and the removal effect of the system on pollutants was investigated.Then,for the A2/O-MBR combined process effluent,through the test of chemical dephosphorization and denitrification deep bed filter,the continuous operation characteristics of the integrated system are investigated to ensure that the final effluent meets the A standard discharge requirements.In order to further investigate the long-term operation characteristics of A2/O-MBR combined process for treating urban domestic sewage and improve the effect of nitrogen and phosphorus removal,orthogonal experiment was used to analyze the influence of various control parameters on the effluent TN concentration and membrane specific flux.For the treatment effect of COD,NH4+-N,TN,TP and SS,the optimal operating parameters of the A2/O-MBR combination process are determined.The results show that the optimal operating conditions of the system are 20:1,the MLSS is 8000-10000 mg/L,and the average removal rate of COD,NH4+-N and SS is 92.8%,98.87%,95.9%,when the reflux ratio is 250%,all meet the Tianjin local A standard discharge requirements.The removal effect of TN and TP in the effluent is not very good,and it is difficult to meet the A standard emission requirements.In order to achieve higher emission requirements,deep nitrogen and phosphorus removal is required.The chemical dephosphorization process was used to deeply dephosphorize the effluent from the A2/O process.The effect of different PAC dosages on the TP treatment was investigated.The optimal dosage of PAC was determined to be 30 mg/L.Continuous operation for 50 days under the optimal dosage,the phosphorus removal effect is stable.The effluent TP concentration was 0.24 mg/L,and the average TP removal rate reached 87.1%,which satisfied the A standard.At the same time,the effects of chemical phosphorus removal on the performance of MBR were analyzed,including membrane fouling and changes in the sludge mixture in the MBR tank.For the denitrification stage of the deep-bed filter,sodium acetate is used as the external carbon source to control the influent water C/N of 4:1,and the filtration rate is 0.6 m/h,which can satisfy the effluent TN<10 mg/L.Based on the optimization of three units of A2/O-MBR process&chemical dephosphorization&deep bed filter,the continuous operation characteristics of the combined process were investigated.The test results show that the combined process is COD,NH4+-N,TN in wastewater.The average removal rates of TP and SS reached 95.43%,98.97%,91.0%,97.32%and 95.5%,respectively.The removal effect of pollutants was good,and the effluent concentration of various pollutants could meet the pollutants of Tianjin Municipal Wastewater Treatment Plant.Emission standards for the A standard in the Emission Standards(DB12/599-2015).