The Study On The Sewage Treatment Performance By Using Vertical Constructed Wetland

This study aims to explore the use of vertical flow constructed wetland in treating sewage applications. Simulate influent based on sewage. Study the operation and performance of vertical flow constructed wetland. Study the remove performance of pollutions in sewage by changing the wetland water level and C/N ratio, in order to support the application of vertical flow wetland in treating sewage. The main conclusions of this study are as follows:(1) Both the peak time and mean residence time of each constructed wetlands are smaller than the theoretical residence time of 4 constructed wetlands. It has "short flow" in vertical flow constructed wetlands. There’s "dead zone" in the upper part of each vertical flow constructed wetland, and in the lower part has "short flow". After analyzing the hydrodynamic conditions in different reactors we find that in large porosity filter wetland system is easier to form a "short flow", the water flows through the different types of filler layer is also easy to form "short flow".(2) The water-saturation level has a obvious effluence on the performance of each constructed wetlands.The ammonia removal rate has a increase with the decrease of water level, and the removal rate is significantly higher when the reactor runs at low water level (2 cm, 19 cm). The best case of ammonia removal appears when water level is 2 cm. The highest removal rate can reach 88.79%.The nitrate removal rate has a decreased with the decrease of water level generally. When the water level is higher than 36 cm, each reactor’s nitrate removal rate are maintained at a high level, the average removal rate is over 80.18%. The nitrate removal rate reaches the highest level, when the reactor s operated at full water level. At the same time, the nitrate concentration fluctuations in effluent of each reactor because of the reaction ANAMMOX (anaerobic ammonium oxidation).The accumulation of nitrite is less in vertical flow constructed wetland. The nitrite concentration is very low or undetectable except at the low water level.The total nitrogen removal efficiency is good in all vertical flow constructed wetland reactors except CW4. Especially at the higher water level, the average removal rate is above 58.22%. When the water level height is 36 cm, total nitrogen remove performance reaches highest, the removal rates are 77.58%,77.18% and 76.08%.The results of the experiment evaluate the behavior of pollutants removal from vertical flow constructed wetland reactors suggest that, the removal progress of total nitrogen is simulate to ammonia and nitrate, it mainly occurred in the upper part of wetland water body, the area from the water surface to the second sampling port.The total phosphorus removal efficiency is good in all vertical flow constructed wetland reactors except CW4, the removal rate is over 70.33%. The removal progress of total phosphorus is basically related to the sampling ports’height in media, rather than the water level.The COD removal efficiency is good in all vertical flow constructed wetland reactors the average removal rate is above 51.62%. The COD removal rate has a decreased with the decrease of water level generally. The removal rate reaches the highest level when the water level is low, and the highest removal rate can reach 86.02%. We can see that the removal progress of COD is simulate to total nitrogen, it mainly occurred in the upper part of wetland water body, the area from the water surface to the second sampling port.(3)When rise C/N ratio in influent, the removal rate of ammonia has an obvious drop, ammonia nitrogen removal rate fell to 28.66%～44.09%from 47.09%～51.62%, the removal rates of nitrate have increase and decrease, but the change is not obvious, therefore, the removal rate of total nitrogen also has an obvious drop, removal rate fell to 56.30%～61.86%from 63.73%～69.80%.While all reactors’COD removal rate has a increase with the rise of C/N ratio except CW1.(4)The pollutants removal efficiencies are different between different filters. The experimental results show that the slag is a better choice of constructed wetland filter than gravel, and a smaller size is better.(5)The pollutants removal level maintains at a high level when the temperature is 11℃,while the removal rate decreased obviously when the temperature drops to 2 ℃.The performance of constructed wetland is poor when temperature is low.