| Water environment problems like water pollution and ecological destruction affect the economic development of production and life of the people. The horizontal subsurface flow constructed wetland could effectively remove pollutants in wastewater and repair damaged aquatic environment as a new cost-effective wastewater treatment technology. In this study, the nitrogen and phosphorus removal efficiency and effects of hydraulic loading, operating water level of wetlands, pollution load on the removal efficiency in the intermittent aeration horizontal subsurface constructed wetlands were studied. Relations between removal efficiency and dissolved oxygen were also detected by changing the aeration time, aeration intensity and aeration methods. N2O flux of the constructed wetland in the case of intermittent aeration conditions and normal conditions were studied to provide greenhouse gas emissions basic data. The main research conclusions are as follows:(1) Pollutant removal of intermittent aeration wetlands was significantly higher than conventional constructed wetlands. The COD, ammonia nitrogen, total nitrogen and total phosphorus average removal rates of the intermittent aeration wetlands were87.37%,81.38%,73.57%and62.58%, respectively, which were1.17,2.17,2.45,1.9times of the normal wetlands respectively. Intermittent aeration greatly improved the efficiency of pollutant removal. Hydraulic loading, pollution load and wetlands operating water level could affect purifying effect.The optimum hydraulic loading was10cm/d, and the optimum operating water level was60cm for the horizontal subsurface flow constructed wetlands.(2) Removal efficiency of the intermittent aeration wetlands when aeration gas-water ratio was set as2,4,6,8,10,12,15was studied. It was found that the removal of pollutants would increase when gas-water ratio increased within a certain range. But the removal efficiency would not increase beyond a certain range of gas-water ratio. The optimum aeration gas-water ratio was10. Removal efficiency when total aeration time was set as4,6,8and12h was researched. And the optimum aeration time was8h. Removal of pollutants between intermittent aeration wetlands and continuous aeration wetlands were compared. It was found that COD and ammonia nitrogen removal of continuous aeration wetlands were slightly higher than the intermittent aeration wetlands, but the total nitrogen removal rate was slightly lower. The total phosphorus removal made no significant differences(3) Intermittent aeration wetlands and conventional subsurface flow wetland showed significant release of N2O, but the N2O flux of the intermittent aeration wetland N2O flux was significantly higher than that of conventional subsurface wetlands. N2O flux of the intermittent aeration wetlands and conventional wetlands were64lμg/(m2·h) and443μg/(m2·h) on average, respectively. N2O flux also showed a more significant seasonal variation. Flux in summer was higher than flux in spring and autumn. N2O Flux also showed significant daily variation. Range of N2O flux for the intermittent aeration wetlands and conventional wetlands was334.7μg/(m2·h)-1014.2μg/(m2·h)and218.4μg/(m2·h)-784.6μg/(m2·h) respectively. N2O flux at noon was higher than flux at night and in the morning. N2O flux change along the way of the wetlands was more obvious, preceding the release of N2O flux in the front of the wetlands was higher than flux in the middle and the back. The abundant preceding organic matter, ammonia and dissolved oxygen for the nitrification and... |
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