Study On The Nitrogen Removal Efficiency Of Constructed Wetland In Zao River

Zao River accepts most pollution of Xi’an city, wastwater is directly dischargedinto Wei River, causing water pollution in Wei River is becoming more and moreserious, in order to improve the water environment of Wei River and its main tributary,the construction of the Zao River Wetland Demonstration Project, through long-termanalysis, in order to find a more efficiency wetlands, provide a model for thecomprehensive management of the Wei River Xi’an segment, and construct wetlandsfor treatment of city sewage and provide the basis for reference use of Xi’an city andnorthwest china.This study selected a surface flow constructed wetland and a compositeconstructed wetland of Zao River Wetland Demonstration Project, each seriestreatment scale is100m3/d, the surface flow wetland plant cattail and reed, while thecomposite constructed wetland plant Cattail, reed and ryegrass. Indicators formonitoring by a year of treatment series water quality and sampling along the waterquality and substrate microorganism, proved the influencing factors of nitrogenremoval in the constructed wetland, wetland measures are put forward to improve thedesign parameters and operation management of nitrogen removal efficiency, resultsshow that:(1) The surface flow and composite constructed wetland of Zao River WetlandDemonstration Project can achieve higher nitrogen removal in the condition oflong-term stable operation and plant growth arrest under the winter (total nitrogentreatment rate between47.76%and56.56%,ammonia nitrogen treatment rate between 57.08%and69.91%in winter).(2) The microbial number of composite constructed wetland is more than surfaceflow constructed wetland. The upper and middle is the main area of nitrification, thelower is the main area of denitrification, this function has important significance toimprove nitrogen removal efficiency.(3)In winter ammonifying bacteria has largest number (106-107/g order ofmagnitude), followed by denitrifying bacteria (105-106/g order of magnitude), and atleast for the ammonia-oxidizing bacteria (10-103/g order of magnitude), while thenumber of bacteria in summer than in winter of the same kind by10to103orders ofmagnitude.(4) It showed a significant correlation between the concentration of dissolvedoxygen and the amount of ammonifying bacteria, nitrosobacteria and denitrifyingbacteria. The ammonifying bacteria and ammonia-oxidizing bacteria showed positivecorrelation with dissolved oxygen, while denitrifying bacteria showed negativecorrelation.The dissolved oxygen is the important influencing factor of nitrogenremoval efficiency of constructed wetlands.(5) The dissolved oxygen concentration in summer is10times higher than it inwinter (summer about4mg/L, winter about0.4mg/L), it showed that plant rootstransport oxygen, has a significant effect on the removal of nitrogen in summer.(6) The nitrification limit nitrogen removal efficiency of wetland in summer,while denitrification is the limiting factors in winter, so increasing nitrification canimprove the summer nitrogen removal efficiency, increasing denitrification canimprove the winter nitrogen removal efficiency. The seasonal adjustment wetlandsflooded depth can improve nitrogen removal rate.