Research On Denitrification Performance Optimization Of Step-feed A/O Process Treating High Ammonia Nitrogen Sewage

The step-feed four paragraphs A/O process was used to treat domestic wastewater.This paper fully discussed the influence of the flow distributionand sludge recycle ratio on system nitrification and denitrification performance,compared the pollutant removal efficiency between the flow distribution coefficient method and the equal flow distribution.The reasons of nitrogen efficiency of two methods were analyzed,the flow distribution and sludge recycle ratio were optimized in order to provide the basis for actual operation.In addition,the sludge properties such as the secondary sedimentation tank sludge height,sludge concentration and SRT were also examined.The main contents are as follows:(1)The flow distribution coefficient method is based on making full use of the carbon in the raw water source.It can satisfy to provide plenty of the electron donor of aerobic area denitrification of nitrate nitrogen in the upper paragraphs,ensures the last paragraph influent at least at the same time and the effluent nitrate nitrogen concentration at lowest.Under the condition of the high C/N,the pollutants removal effect of flow distribution method is superior to the equal flow distribution method.(2)When the flow distribution coefficient method was applied,the nitrogen removal efficiency of the system affected by nitrification and denitrification at the same time at high load.At the low load,the nitrogen removal efficiency of system affected mainly by denitrification.The nitrate nitrogen concentration of the aerobic zone was higher and effluent nitrogen was mainly for nitrate nitrogen.COD removal efficency of low load condition was better than that of high load condition and the remaval rate in HRT=24h?C/N=10 reached the highest and it was 95.76%.Under low load of diffierent distribution ratios,ammonia nitrogen removal rate was higher and stable and all was above 98%;At the high load,because the sysetem total nitrification capacity was enough,the ammonia nitrogen removal rate was 97.63%and higher than the equal flow distribution.In load C/N,the effect of the flow distribution on TN removal rate was little;Under low load and high C/N,the nitrification and denitrification of system paragraphs were completely,while the total nitrogen concentration was minimum and the highest TN removal rate was 93.21%.Therefore,at low load highC/N,adopting the flow distribution coefficient method could achieve good pollutant removal effect.(3)Under different sludge reflux ratios,COD concentration of each processing unit changed little and R had little impact on COD removal efficiency.In the raw water,COD got removed though dilution,denitrication and assimilation.With the increasing of R,NH3-N and TN removal efficiency presented downward trend after rising first.Ammonia nitrogen removal rate reached the highest and was 96.89%when R=1.00;TN removal rate reached maximum and was 84.57%when R=0.75.Therefore,in the step-feed A/O process,the sludge reflux ratio was appropriate to increase in a certain degree to add the microbial quantity of refluxing sludge,while the denitrification ability of first paragraph anoxic zone was fully used,but the sludge reflux ratio should be controlled below 1.0.(4)The higher sludge reflux ratio was unfavorable using at a higher sludge SVI,because of aggravating the sludge expansion.In addition,the higher sludge reflux ratio would reduce the system's components gradient of suspended solid,which changes the system processing capacity.At the same time,the system solid residence time was reduced following R increasing,affecting the sludge population structure to a certain extent.