| With the outburst development of the social economy, a large quantity of untreated and/or poorly treated domestic sewerage, industrial wastewater and non-pointed pollution were discharged into lakes, which resulted in serious eutrophication of Lake Tai.One of the main reasons for the Lake Tai eutrophication is the large quantity of N and P contained in the rivers which entering the lake. Therefore, it is utmost important to effectively reduce N and P in the rivers in order to relive the lake eutrophication. This thesis is based on the Project of Environment Friendly Drainage an Ecologic Recovery of Heavy Polluted Sediments, the third sub-project of Technology and Demonstration Project of Water Pollution Control and Water Quality Recovery at Lake Tai, sponsored by the Ministry of Science and Technology as a special project for Lake Tai(2002AA601013).In consideration of lakeside properties and landscape, with the constructed wetlands, the effect on N and P distribution and removal efficiency of the plants, matrices and the root zone microorganism and the process mechanism were intensively investigated in this experimental research.The highest percentages of TN and TP removed by constructed wetlands were 81% and 15%, respectively, among them 7.4%～7.9% TN and 5.23%～5.77% TP were removed through plant (Phragmites australis and Typha latifolia,)assimila.tion, 3.9% TP were removed by matrices adsorption(gravel).Root zoon effects were highly obvious in the constructed wetlands, with thequantity of heterotrophic bacteria up to 106-108 cell g-1 in root zoon. The quantity ofnitrifying bacteria on root was 10-folds that on matrices. And , he quantity of nitrifying bacteria on zeolite of root zoon was 1.5～3.0 folds that on slag.TN removal efficiencies changed with quantity of nitrifying bacteria on root zoon, temperature, dissolved oxygen contents, root size, which indicated that microbes in root zoon played an key part in nitrification and denitrification processes of constructed wetlands.With rather lower ratio of organic carbon and total nitrogen, nitrogen removal processes had been completed efficiently and steadily, which resulted from the different nitrogen removal mechanisms between the constructed wetlands and A/O wastewater treatment system. Substances secreted by plants and degradation products of plant debris could be one kind of carbon sources used for denitrification.TP removal efficiency decreased with the time of matrices used. That indicated sustainable adsorption capacity could only be got by matrices renewal.Though direct removal percentages of TN and TP by plant assimilation and adsorption were rather limited, the indirect effects imposed by plant and matrices on root zoon microbial ecology were very strong. More oxygen could be supplied by plant photosynthesis and also by sequential inflow and outflow. |
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