Purification Of Micro-polluted Water By Constructed Wetland

In order to show a better guidance to the demonstration project and the actual project, we established four constructed wetland system with the fillings which were selected from Tianjin. The purification of micro-polluted water was studied in both cases of no plants in winter and with plants in summer. And the resistance of storm water pollution in rainy season was studied also in this paper.Compound soil, haydite, shale, quartz sand and gravel fillings were used in this study to establish four complex vertical wetland modes. The purification effects of artificial wetland on light polluted water (eutrophied water in Qingnian Lake in one University) was investigated under the loading surface is 0.95 m3/m2?d. Water quality indicators are chemical oxygen demand (CODCr) 46-176 mg/L, total nitrogen (TN) 2.53-9.27 mg/L, total phosphorus (TP) 0.14-0.60 mg/L, suspended solids (SS)<110 mg/L.The experiment process was divided into 4 stages: Operation debugging; operation phase without plants; operation phase with plants; rain-water purification test.Results showed that in each reactor, the purification effect was better from top to bottom, which means in the bottom had the best quality water. But the removal of pollutants was not enhance so dramaticlly between the medial and bottom layers, therefore, considering on economy and purification effect, the deepest layer should be 0.9 meter or so.Compared with the purification effects without plant, it can be concluded that the combination of quartz sand, shale and gravel has the optimum effect on removing TN, ammonia, and COD, the average removal is 31.68%, 84.26% and 68.72% respectively. While the combination of quartz sand, haydite and gravel has the best removing effect for TP, the average removal is 65.74%; Shale has a better effect on removing ammonia and COD than haydite.Plant has a significant influence on wetland purification effect, especially on the removal of TN and COD. Phragmites Australis has a better purification effect than Iris Pseudacorus on the removal of TN and COD, but as to TP it is worse than Iris Pseudacorus. The experiment results show that wetland can not only deal with lake water in dry seasons, but also enhance the purification effect on the heavily polluted initial rain-water by resisting the pollution loading caused by initial rain-water flushing in raining seasons.