Commissioning And Operation Of Composite Constructed Wetland Purification System Of The Terminal Effluent From Sewage Treatment Plant

In recent years,with considerable sewage treatment facilities are built,the sewage treatment capacity has increased significantly in China.However,the terminal effluent from sewage treatment plant has the characteristics of high nitrogen and phosphorus concentrations,which will still cause eutrophication and pollution when discharged into water.Therefore,Studying the deep removal of nitrogen and phosphorus in terminal effluent from sewage treatment plant is of great significance to improve the water environment in China.Our team constructed a composite constructed wetland system with treatment capacity of 5000m3/d as the deep purification for the terminal effluent from Yixing urban sewage treatment plant and attempted to use building waste blocks as the main substrates to explore the effectiveness of"treating waste with waste".In this paper,we made the study about the purification effect of the composite constructed wetland system of the terminal effluent from sewage treatment plant for 8 months（232d）,including its commissioning and operation.It is expected to provide a new reference for deep purification of terminal effluent from sewage treatment plant and application of constructed wetland technology.The conclusions are as following:（1）The phosphorus removal rate of building waste block was 40%,which is higher than that of gravel（The phosphorus removal rate was 10%）.And the release rate of building waste blocks for phosphorus is lower（the release rate was 15%）.Therefore,using building waste blocks as wetland substrates could effectively remove phosphorus in the terminal effluent.（2）After 46 days,the wetland system commissioned.The system average removal rates of TN,NH₄⁺-N,NO₃^--N,COD_Crr and TP during the commissioning period were 13.5%,19.5%,12.5%,25.1%,and 36.7%,respectively.The removal rate of pollutants(except COD_Cr)gradually increased during the wetland operation period,and the removal rates of TN,NH₄⁺-N,NO₃^--N,TP increased from 17.6%,25.9%,15.9%,63.7%of the transitional period to40.0%,31.2%,46.4%,68.7%of the stable period,respectively.（3）There was a certain difference in the pollutant removal effect of each unit during the stable period.Every unit could make further improvement on TN and NO₃^--N,and bio-film wetland system（such as C,D,etc.）was more effective in removing TN,NO₃^--N and TP than surface-flow wetland system（such as A,F,etc.）.The removal of NH₄⁺-N and COD_Crr was mainly by fore units of the wetland system.Because of the different constructions,the baffled submerged flow unit（D）was more effective in removing in TN and TP than the bottom diversion submerged flow unit（E）,but the latter TP removal rate of each unit area was higher than the former.（4）Using building waste blocks as the main substrates,the construction cost（20-30%）of the wetland system could be cut down.However,due to the waste blocks itself adsorbed some pollutants,the commissioning time of the wetland system will be prolonged,which will also affect the pollutant remove rate of the wetland.So it should be used with caution in actual project.