Interception Effect Of Rural Sewage By Constructed Wetland System In Subtropical Hilly Region

In recent years,the issue of water pollution caused by agricultural non-point source pollution has drawn increasing attention.The random discharge of a large amount of untreated rural sewage has resulted in serious eutrophication of rivers and lakes.As a low-cost,easy-to-operate and well-treated wastewater treatment technology,constructed wetlands are widely used in the prevention and control of non-point source pollution.M.elatinoides is a perennial submerged or floating herbaceous plant with strong absorption capacity of nitrogen and phosphorus（NP）and high tolerance to high ammonia nitrogen（NH₄⁺-N）.At present,most of the reports on treatment of rural sewage by M.elatinoides are short-term indoor simulation tests,and there are relatively few reports on the long-term field application of high-load rural sewage.Based on this,through the combination of field control test and positioning test,the removal efficiency of constructed pollutants in constructed wetlands was analyzed by monitoring the changes of NH₄⁺-N,TN,TP and COD concentrations in effluent,Volume and sediment NP content of the spatial and temporal changes,the main way to resolve pollutants removal;by measuring the dynamic changes of pH,DO and Eh in water,to identify the key factors affecting the removal of pollutants in the M.elatinoides wetlands in order to optimize the environmental factors Constructed wetlands field application to provide a scientific basis.The main conclusions of this thesis are as follows:1、Study on the Removal Ability of M.elatinoides Wetland System on Rural Domestic WastewaterPlanting plants in constructed wetlands could significantly improve TN,TP and COD removal efficiencies in wetland systems.Compared with no-plant systems,planting M.elatinoides in wetland systems could increase TN removal efficiency by 33.5%and TP removal by 40.1%,34.5%of the removal rate of COD;the average removal rates of TN,TP and COD of rural domestic sewage were 50.9%,93.4%and 79.3%respectively,significantly higher than 61.8%,79.3%and 53.8%of CK（p<0.05）.The accumulation of NP in the M.elatinoides was significantly higher than that of the weeds（p<0.05）.Therefore,the M.elatinoides was more suitable as a wetland plant to treat rural domestic sewage.2、Study on the Removal Ability of Combined-mode Wetland System on Rural Domestic SewageThe removal rates of TN,TP and COD in wetland of each plant were in the range of 89.8%-97.8%,54.7%-81.3%and 61.7%-96.3%.respectively.The removal rates of COD was the best by M.elatinoides and C.palustris composite pattern,The removal rates of TN was the best by M.elatinoides and H chinensis composite pattern,The removal rates of TP was the best by M.elatinoides and P.cordata composite pattern,N and P accumulation quantity were the most by M.elatinoides and P.cordata、M.elatinoides and S.stoloniferum combination pattern was significantly higher than that of the other 4 plants（p<0.05）.3、Application of M.elatinoides Wetland Technology on High-load Rural Sewage Treatment.The M.elatinoides wetland system has a good removal effect on farming wastewater and rural domestic sewage.The NH₄⁺-N,TN,TP and COD of the wastewater from wetland farming can all reach the standards of "Emission Standard of Pollutants for Municipal Wastewater Treatment Plant"（GB18918-2002）.The effluent of rural domestic sewage wetlands can reach Grade A standard except for TP,while plant absorption and sediment absorption are the important ways to remove NP of wetland system,accounting for the removal of NP of domestic wastewater and domestic wastewater wetland system respectively 21.6%,22.8%,18.7%,62.7%and 30.9%,33.4%,21.8%and 55.5%respectively.The concentrations of TN and TP in culture wastewater and domestic sewage wetlands were negatively correlated with Eh and DO（p<0.01）.Significant positive correlation（p<0.01）,and also showed a significant correlation between environmental factors.