Study On The Function Of Nitrogen Removal In Subsurface Flow Constructed Wetlands

Constructed wetland is a kind of strengthen natural processing technique, has been extensive applied in North America, Europe and other Western Country, but still at the developing stage in China. In the different constructed wetlands, subsurface flow wetland is the main type in engineering application because of its high hydraulic and contaminative burthen. The room of aerobic, anoxic and anaerobic where happen at floristic rhizome, provides a good condition for nitrogen removal in subsurface constructed wetland. And factor, mechanism, mathematic model of nitrogen removal in constructed wetlands have become the main study points to different scholars.In this paper, subsurface flow wetland(SSFW) was the main study object, at the same time, discussed the optimal hydraulic burthen and contaminative removal efficiency in different floristic constructed wetlands. Farther studyed on hydraulic burthen, C/N, the source and concentration of carbon, the source and concentration of nitrogen which effected on nitrogen removal in Spathiphyllum kochii and Acorus gramineus constructed wetlands. At last, discussing mechanism of nitrogen removal based on analyzing the different depth of padding in the subsurface flow constructed wetlands.Experiment result: different floristic subsurface flow constructed wetlands could achieve high COD and nitrogen removal efficiency in the low hydraulic burthen and contaminative burthen, the efficiency basic maintained about 90.0%. The removal efficiency of flourishing Acorus gramineus constructed wetland was higher than Spathiphyllum kochii wetland. But, the higher hydraulic and contaminative burthen, the lower removal efficiency in different wetlands; the lowest removal efficiency of NH₄⁺—N just achieved 75.0% in the experimentation of two kinds of wetlands. When plant growing further mature, the result of decontamination surpassed to initial stage. From the experiment, the optimal hydraulic burthen among 0.15m³ /m² d～0.20m³/m² d in the subsurface flow wetlands .The main factor effected on the result of decontamination was C/N(TN) in the SSFW. When keeping the concentration of TN invariable, and increasing the concentration of carbon, along with the increasing C/N, ammonia nitrogen and COD removal efficiency descended obviously, and the lowest COD removal efficiency just reached 81.28% or so. But to TN removal, under lacking of carbon, the result of decontamination in the two kinds of wetlands were bad, the highest was about 60.0% and the lowest only had 32.0%. Along with increasing carbon, the TN removal efficiency of two kinds of wetlands were going up. When the C/N=10:1, the TN removal efficiency in Acorus gramineus constructed wetland could reach 83.52%, and the Spathiphyllum kochii wetland also achieved 73.71%. C/ N=7:1～8:1 as the best in this experimentation.From the result of decontamination in different depth of padding in different subsurface flow wetlands, COD and NH₄⁺—N had been decomposed through oxidation around floristic rhizome, and denitrification happened at the room of anoxic and anaerobic where far from the floristic rhizome. But in the plenteous of carbon, TN removal efficiency could achieve a good decontaminating result in the room of aerobic around floristic rhizome.Much factor can effect on the ability of nitrogen removal in SSFW, if wetlands are made up of different padding and different plant, their nitrogen removal efficiency maybe strong difference; outside factor such as: concentration of DO, temperature, pH and so on, also add a certain influence on the ability of nitrification—denitrification in constructed wetlands; the unreasonable design can impact of nitrogen removal in wetlands too. So, the ability of nitrogen removal in constructed wetlands need to be comprehensive considerated. Experimentation indicated that nitrogen removal in subsurface flow constructed wetlands might through nitrification—denitrification by nitrite, anaerobic ammonium oxidation and simultaneous nitrification—denitrification at the same time.