The Study On Optimazation Of Biological Nitrogen And Phosphorus Removal In Urban A~2/O Wastewater Treatment Plant

In this study,based on the analysis of influent and effluent characteristics and process problems of the typical WWTPs using A~2/O process in Taihu basin,the efficiency of nitrogen and phosphorus removal and the process optimization of two typical urban WWTPs were studyed.The conclusions are as followed:In this study,two typical urban WWTPs were chosen to conduct the anylysis of the efficiency of nitrogen and phosphorus removal and the process optimization,based on the analysis of the typical WWTPs applying A~2/O process on water characteristics and process problems in Taihu basin.The conclusions were made as following:1)According to analysis of influent and effluent characteristics and ratio of carbon to nitrogen,it showed that: In the influent of WX-A WWTP,TN and NH3-N were influenced remarkably by seasonal change,while COD and TP were relatively stable.The annual average of COD/TN was greater than 7,BOD/TN was higher than the minimum requirement of biological nitrogen removal(BOD/TN?3).COD and NH3-N could reach the standard stably,TN was vulnerable to the influence of low temperature in winter,TP was stable below 0.6 mg/L,the biological phosphorus removal ability was normal.In the influent of WX-B WWTP,TN,COD and NH3-N was seasonal fluctuated.According to the influent fluctuation,COD and TP were intermittent remarkably,The annual average of COD/TN was greater than 6,BOD/TN was greater than 3.TP and COD could reach the standard stably,chemical phosphorus removal was stable,biological phosphorus removal was not obvious,TN was difficult to reach the standard.2)According to measurement of carrying oxygen in the recycling mixture,it showed that: the average concentration of DO in the recycling mixture was greater than 3 mg/L,and the WXB WWTP reached 4 mg/L or more.The effets of carrying oxygen in the recycling mixture on denitrification in anoxic tank was studied,the result showed that: under the static test condition,2# without oxygen removed 1.70 mg/L NO3--N more than 1# with oxygen;under the dynamic test condition,1# removed 1.02 mg/L NO3--N less than 2#,combined with the amount of water in the reactor,it was higher than static test condition.there may be some other factors influenced the efficiency of nitrogen remove.Value k of model which was used to forcast effets of carrying oxygen in the recycling mixture on denitrification in anoxic tank was studied,the results show that: value k affected remarkably by recycling mixture ratio,and HRT has little impact on value k.Value k could choose 1.1~1.3 in the engineering.The higher recycling mixture ratio,the higher value k.3)Based on the problem of recycling mixture with oxygen,the oxygen consumption rate at the end of the aerobic tank mixture was studied,and suggestions of setting oxygen elimination area was put forward: WX-A WWTP oxygen consumption rate is 6.44 mgO2?g-1MLVSS?h-1,WX-B WWTP oxygen consumption rate is 5.63 mg O2?g-1MLVSS?h-1.It could choose 20 min as design parameters of oxygen elimination area.4)The dynamic analysis of the features of TP in the full process was done in the WWTP,the result showed that: 1#the biological system without PAFC had showed a certain phosphorus releases capacity,but not obvious in the anaerobic tank.2# with PAFC had not showed a obvious phosphorus releases capacity.The effect of PAFC on the characteristics of the whole process of TP in the chemical treatment plant were analyzed.The results showed that the WXA WWTP,the biological system has a certain phosphorus releases phosphorus releases capacity,but the anaerobic phosphorus releases is not significant.The effection of chemical medicament of phosphorus removal on biological phosphorus removal was studied.The results showed that chemical medicament of phosphorus removal has no significant influence on biological phosphorus removal and the existence of PAFC has no influence on biological phosphorus releases.The biological phosphorus releases couldn't be detected in the experiment group and the control group.Microbiological characteristics of activated sludge from the process of synergistic chemical phosphorus removal was analysed,the results showed that WX-B WWTP exist two strains of PAO in the activated sludge.The phosphorus removal efficiency of two strains of PAO was more than 90%.