| In recent years,with the rapid development of the rural areas in the Taihu Lake,the pollutant of rural disorderly discharge wastewater have become the important non-point pollution sources of nitrogen and phosphorus load of the water body.The pollutant concentration was high and the concentration of TP?TN and COD were 0.01mg/L?3.52mg/L?0.20mg/L?26.20mg/L and 8mg/L?326mg/L.For the rural disorderly discharge wastewater have characteristics of unstable quality and high concentration,so a modified subsurface wetland—"Aerobic/anaerobic/aerobic three-step aquatic vegetable wetland"(O-A-O aquatic vegetable wetland).It used to intercept and remove nitrogen and phosphorus pollutants into Taihu Lake with building the demonstration project with taking O-A-O aquatic vegetable wetland as the core technology in Yixing Gedu natural villages.This paper studied the process characteristics and the mechanism of nitrogen and phosphorus removal of the new wetland,and monitoring the long-term operation effect of Gedu demonstration project It has made the following main conclusions:1?The pollutants purifications of three kinds wetlands(common subsurface wetland?O-A-O aquatic vegetable wetland?no plant wetland)were compared during May to August and the result showed that the O-A-O wetland has the greatest consolidated removal rate.Removal rates of COD?TP?NH4+-N?NO3--N and TN were 50.72 ±2.33%?81.70±1.29%?76.64±3.56%?89.78±2.00%and 67.68±3.09%.Their effluent concentration were 40.7±10.1mg/L?0.08±0.03mg/L?0.52±0.08mg/L?0.27±0.07mg/L and 2.01±21mg/L.2?The characteristics of O-A-O aquatic vegetable wetland for nitrogen and phosphorus were fully manifested.The best HRT of O-A-O aquatic vegetable wetland was 20h and the removal rate of TN and TP were 69.93%and 82.13%.When the HRT was constant,there is no correlation between TN and TP's removal rate and their influent concentration in a certain concentration range.Moderate harvest frequency of spinach had enhancement impact on removing nitrogen and phosphorus.3?The mechanism of O-A-O aquatic vegetable wetland removal of nitrogen and phosphorus was studied by combining field test with indoor simulation studies.The results showed that the performance of removing phosphorus by matrix was better than removing nitrogen.Compared with NO3--N,spinach had stronger sbsorption ability of NH4+-N.The absorption rate of phosphorus by spinach was 0.12mg/(g·d).The denitrification intensity of middle section(anaerobic section)was 40.08mg/(kg h)and its was the highest of three sections.The mainly removal of nitrate nitrogen was in the anaerobic section and its contribution rate of removal can reach 79.82%.The amount of nitrogen removed from wetland by denitrification and other removal routes during the operation was 1414g,accounting for 59.34%of the total removal of nitrogen,which was 23.8%and 54.22%higher than that of plant uptake and matrix adsorption.The sedimentation and adsorption of matrix was the most important way to remove phosphorus from wetland,and the total amount of phosphorus removed by this pathway was 59.97%.4?After monitoring the long-term operation effect of Gedu demonstration project,the result showed that rural disorderly discharge wastewater was interfered by the ecological ditches,reservoirs and O-A-O aquatic vegetable wetland,the average removal rate of TN and TP was higher than 60%,80%.As the core technology of demonstration project,O-A-O aquatic vegetable wetland can effectively reduced the nitrogen and phosphorus load into the Taihu Lake. |
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