| Even after some treatments having been taken in the Eleventh Five-Year Plan period, the lake eutrophication is still rather serious in China, which remains one of the most arduous tasks for the water environment scientists to solve urgently. The water quality of Lake Erhai, which is a typical lake in the early stage of eutrophication, has turned better under powerful treatments. But if the pollutants load into the lake increases, the lake will tend to be in an eutrophication state. Hence the analyses and researches about present status of water pollution of Lake Erhai and control technologies are of great significance in controlling increasingly serious tendency of eutrophication in Lake Erhai and providing important references to other lakes in China.Currently, with the accomplishment of the major projects in the Eleventh Five-Year Plan, the focus of pollution control in the Lake Erhai watershed shifts from centralized pollution treatment constructions to the comprehensive treatments of low pollutants concentration but high load inflow rivers and low pollution water.In this thesis, the pollution characteristics of north Erhai inflow rivers and the load reduction of wetland have been analyzed, and the treatment effect of the constructed wetland to inflow low pollution water has been studied. By adding measures like aeration, pollutants removal efficiency of constructed wetland pilot has been raised. Therefore, a set of worth popularized low pollution water treatment technologies in the Lake Erhai watershed is formed. The main research contents include: (1) Luoshi River and Yongan River, the two main rivers in the northern part of Erhai watershed, have been selected as the research objects. By analyzing the pollution of Luoshi River and Yongan River from aspects of space and time using Applying Mark Index method and Equivalent Standard Pollutant Loading method respectively, the main pollutants, main polluted zones and pollution characteristics of different periods can be found. (2) The water qualities of Deng Beiqiao Wetland and The Luoshi River Estuary Wetland have been monitored regularly. Compared the water quality data of wetlands with those of the two inflow rivers, the present wetlands'treatment efficiency of the low pollution water can be analyzed. (3) Constructed wetland pilot has been built. The pollutants removal effect of the pilot has been compared with that of wavy subsurface flow constructed wetland(W-SFCW) and subsurface flow constructed wetland(SFCW),and researches on the increasing of organic matters, ammonia and total nitrogen removal effect through enhanced aeration have been done.The research indicates that, the general water quality of the Luoshi River and the Yongan River wasⅤand >Ⅴrespectively, which were both worse thanⅢ. The major polluting time period was in Spring and Summer, and the major pollutants were total nitrogen and total phosphorus. It is estimated that, in 2010, the load of the total nitrogen and total phosphorus into the lake was 129.5t/a and 5.1t/a, respectively. In conclusion, through the treatments of several pollution treatment projects, the water quality of the two inflow rivers has improved in some extent, and the water quality can reachⅢat the estuary. But the overall water quality is still not good and fluctuates in the whole year.Deng Beiqiao Wetland and Luoshi River Estuary Wetland treated wastewater from Yongan River and Luoshi River respectively. We can concluded that the outflow from Deng Beiqiao Wetland was better thanⅢall year, which was the same of that from Luoshi River Estuary Wetland, except TN, TN and TP load reduction by Deng Beiqiao Wetland was 7.3t/a and 0.42t/a, respectively. In Luoshi River Estuary Wetland, the amount was 38.4t/a and 2.1t/a, respectively. The result of constructed wetland pilot shows that, wave-subsurface flow constructed wetland is better than horizontal subsurface flow constructed wetland. Enhanced aeration can improve the removal of NH4+-N and TN effectively. The average removal efficiency of TN rises from 38.7% to 86.5%, and meanwhile that of NH4+-N rises from 16.3% to 82.3%. |
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