Study On Adding Solid Carbon Source To Strengthen Denitrification In Constructed Wetland

Constructed wetland has a simple process,good purification effect,and the advantages of convenient operation and management,investment at home and abroad has been widely used in polluted water treatment,but in the treatment of low C/N wastewater,required in the process of denitrification carbon source shortage will affect the constructed wetland nitrogen removal efficiency of pollutants.In order to improve the removal efficiency of total nitrogen by adding carbon source,the experimental study was carried out on the problems of TN removal rate in the treatment of low C/N wastewater.Select common reed stalks,reed withered leaves and cattail leaves in the wetland as supplementary solid carbon sources,experiments were conducted to determine the carbon source release pattern of different pretreatment plants,scanning electron microscopy was used to observe the surface structure of carbon sources in different pretreated plants,analysis of its release,release of C/N ratio,and analysis of the impact of the release of nitrogen and phosphorus on water quality,screening of the best available carbon source form and dosage;Through simulated static denitrification experiments on different pretreated reed stalks,reed leaves,Cattail leaves and analyze the denitrification performance and denitrification stability of different pretreated plant carbon sources;Construct a horizontal subsurface flow constructed wetland test device,add the selected carbon source to the wetland,and study the effect of the addition of the plant solid carbon source on the removal efficiency of the constructed wetland pollutants,analysis effects of carbon sources added in constructed wetlands on the removal efficiency of total nitrogen in different C/N ratios and propose a strategy of replenishing solid carbon source to enhance the removal efficiency of total nitrogen in constructed wetland.The results show that:（1）Changes in surface characteristics of carbon prepared by different pretreatment modes were observed by using scanning electron microscopy,the carbon source,after alkali plant surface structure of alkali and heat treatment have great damage,cellulose is broken,the plant carbon source can release carbon source more easily in the late.（2）The average amount of COD released by three kinds of plant carbon sources after simple treatment,alkali soaking treatment and alkali heat treatment were:Reed straws 28.80,30.40,35.91 mg/（L·d）;Reed leaves 30.39,31.24,39.17mg/（L·d）;Cattail leaves 30.38,31.99,33.89 mg/（L·d）.The average release quantity of TN was:reed straw 1.46,1.33,1.07 mg/（L·d）;Reed leaves 1.79,1.54,1.37 mg/（L·d）;Cattail leaves1.81,1.62,1.56 mg/（L·d）.Alkali heat treatment reed straw can release more carbon source,lower nitrogen,phosphorus,C/N higher.It is suitable as a carbon source of denitrification in artificial wetland system.（3）Static denitrification experiments showed that the alkali reheat treated reed straw could continuously enhance the denitrification capacity of the system.The average removal rate of NO₃^--N was the highest in the running 44day.Alkali soaking,alkali heat treatment of reed leaves,cattail litter in the early denitrification effect is good,but the long-term effect of nitrogen is not stable.three kinds of pretreatment,the average removal rate of NO₃^--N were:reed straws 19.45%,78.06%and 85.65%;reed leaves 57.19%,58.63%,60.10%;cattail leaves 35.36%,68.88%,70.20%.The rate of denitrification of reed straw by alkali heat treatment was the highest.three different pretreated plant carbon sources have the ability to stabilize the pH value when denitrifying carbon sources and biological carriers.The accumulation of NO₂^--N in the effluent of alkali soaking and alkali heat treated plant carbon source was significantly lower than that of plant carbon source with simple treatment.（4）Without significantly increasing the effluent COD concentration of the system.,adding alkali heat treatment reed straws carbon source compared with the blank wetland,the removal rate of TN increased from 23.12%to 62.48%,the removal rate of TP increased from 25.32%to 41.33%,adding carbon source to a simultaneous removal of nitrogen and phosphorus removal effect to.The removal rate of NO₃^--N increased from 16.57%to 71.63%.The addition of carbon source effectively promoted the denitrification of microorganisms in the constructed wetland system,and improved the TN removal effect of the wetland system.The removal rate of NH₄⁺-N increased from48.44%to 54.47%.（5）In the wetland system adding carbon source to C/N for 5.5 and 7 can significantly increase the concentration of COD in the wetland,the effluent COD concentration is almost the same as when the carbon source is added to C/N is 4,it will not result in a significant increase in the effluent COD concentration of the wetland system,indicating that the constructed wetland system has a strong impact resistance to COD.（6）Adding carbon source to C/N=5.5 in wetland system is not only conducive to nitrification,but also provides enough carbon source for denitrification reaction,so as to improve TN removal rate in wetland system.When the C/N was 5.5 in the wetland system,the highest removal rate of TN and NO₃^--N was 83.08%,95.47%.（7）With the improvement of C/N in the wetland system,the removal rate of TP gradually increases,indicating that C/N in the wetland system is an important factor affecting the effect of TP removal.