Study On Deep Denitrification Of Tail Water In Sewage Treatment Plant By Autotrophic Denitrification Process

In recent years,the relevant departments of the state have continuously raised the discharge standard of tailwater from sewage treatment plants.However,the tailwater volume of sewage treatment plants is large and the C/N ratio is low.The nitrogen mainly exists in the form of NO₃^--N and its concentration is high,and there is a risk of water quality deterioration when the nitrogen is discharged into the water body.Therefore,it is very important to denitrify deeply the tail water of sewage treatment plant.The current deep denitrification process has problems such as high operating cost and is easy to cause secondary pollution,so it is of great significance to explore an economical and efficient deep denitrification process for tail water of sewage treatment plant in the field of water treatment.In this study,the tail water of sewage treatment plant was taken as the research object.An autotrophic denitrification filter with sodium thiosulfate acts as the sulfur source.Ceramsite and siderite serve as the filler.In order to provide certain technical support for the denitrification process of the tail water of in sewage treatment plant,the denitrification performance and operation effect of the denitrification system were investigated in the present work.The main achievements are obtained as follows.First,the denitrification performance of ceramsite-siderite filter was investigated.Under the domestication of anaerobic sludge,the filter can be successfully started within 12 d,and the removal rate of NO₃^--N in water is stable and reaches over 98%.The optimal operating parameters of the filter are:theoretical dosage of sodium thiosulfate is 1.5 times,hydraulic retention time（HRT）is 2 h,inlet p H is neutral（about 7）and temperature is 30^oC.During the stable operation,the removal rate of NO₃^--N in the filter was 100%,the TN removal rate was more than95%,and the effluent SO₄^2-concentration was≤250 mg/L,and the effluent NO₂^--N concentration was≤0.03 mg/L.Meanwhile,a large number of microorganisms were enriched on the filler surface inside the filter,and siderite filler could also directly participate in the denitrification reaction as an electron donor,further promoting the denitrification effect of the filter.Secondly,the microbial community structure inside the filter was analyzed.The results show that the microbial environment in the filter has high similarity and diversity.The dominant bacteria in the filter are Proteobacteria,Betaproteobacteria,Thiobacillus and Ferritrophicum,and the abundance of the dominant bacteria in the lower part of the filter is the highest.And these two functional microorganisms promote the rapid denitrification of NO₃^--N in the water and ensure the stable and efficient denitrification performance of the filter.Finally,the distribution about treatment efficiency and application of filter are analyzed.The results showed that in the 80cm-high filter,the removal rate of NO₃^--N increased along the path,while the denitrification process was mainly concentrated below 40 cm in the filter,reaching 84.1%.The washing cycle of the filter is 60 d,and the denitrification performance can be completely restored within 7 d.This process can make the removal rate of NO₃^--N reach 100%,TN above 95%;the raw material consumption is 0.042 RMB/t,which has certain application value,and more suitable for deep denitrification of tailwater in sewage treatment plants.