| When used in wastewater treatment, the constructed wetland own many advantages of good water quality of outlet, low cost of construction and daily operation, convenience of management and aesthetic value, especially is consistent with the latest environmental tendency of diminishing and spreading form in national wastewater treatment, and is worthy of popularizing in small and middling cities. However, the pollutant removal efficiency of constructed wetland is greatly affected by such factors as air temperature, characteristic of filling materials in wetland, wetland plants, microorganisms in soil,the evaporation and transpiration of wetland, however these factors limit the further improving of purifying effect in wetland, now becoming the blocking bottleneck in extending application of wetland.Aiming at the affecting factors of nitrogen removal and using the outlet water of prime sedimentation tank as the inlet water of wetland, during the period of Sept.2002 to April.2005, when the contracted wetland were ran in stable conditions, the relation between nitrogen removal efficiency and its impacting factors was studied through the serial constructed wetland. The following experiments are included:(1) the analysis of nitrogen removal effect of different wetland plant, for the first time, the changing laws of photosynthesis and evapotranspiration wetland plants and relation between laws and nitrogen removal effect were studied in experiment, from another point of view the role of plants in wetland nitrogen removal was studied; (2) the wetland filling materials purified pollutants by NH4+-N and TN absorption, and the transforming laws of NO3--N in the process; (3) nitrifying bacteria community were studied by using method of MPN-FISH and statistical data were collected;(4)the study of DO distribution in different plant wetland and its effects on nitrogen removal were discussed; (5)the impacts of wetland construction form, hydraulic condition and operation condition on nitrogen removal were studied all together, ended with some nitrogen removal intensifying experiments.Integrating the experiment data, the nitrogen removal mechanism was studied in details in the paper, by analyzing the function of filling materials, plants and microorganism in wetland it is demonstrated that the photosynthesis and evapotranspiration intensity of wetland plant have great impacts on the nitrogen removal effect, and the total photosynthesis metabolizing capacity could affect the nitrogen removal quantity; the reed has the highest photosynthesis intensity, water use efficiency and large excreting dissolved oxygen in root area; the combination of them have better nitrogen removal efficiency than single one of them, and which is the optimization medium; it is indicated that the cultivating surrounding of nitrifying bacteria was improved and its number was increased too by MPN-FISH analysis; according the"Grey Box"theory, the operation conditions were optimized by the nerve net model, and on the basis the proper feasible methods of intensifying nitrogen removal were put forward. Finally the intensifying methods were tested when the high pollutant concentration wastewater was treated in wetland. Furthermore the phosphorus removal effect and removal mechanism were studied, which maybe helpful to the improving the nitrogen and phosphorus removal together.The nitrogen removal mechanism was studied by suing the experiment achievements in the paper, and the methods of high nitrogen removal efficiency were put forward, which has significant value in popularizing the application of wetlands in varying areas and conditions.
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