| Dianchi Lake is a famous highland freshwater lake and the lake area is about293km2, which is one of the alternate water source in Kunming. With the intensification of pollution in Dianchi Lake, eutrophication of Dianchi Lake increases, the water quality is lower than Grade V. At present, although the Dianchi Lake Basin has been implemented a interception project, in the rainy season, there still exists overflow of interception main canal, which has seriously polluted Dianchi Lake. Therefore, it is necessary to control overflow pollution of Dianchi Lake interception main canal during the rainy season.In this study, in order to achieve minimized pollution load from overflow of interception main canal system of Dianchi Lake,the study on the sources of pollution of Dianchi Lake interception main canal involving drainage areas were investigated and analyzed. Dynamic model of Dianchi Lake interception main canal system was built on the basis of system dynamics method.Through model simulations, impact of different engineering control measures on the on minimized pollutants emission of overflow was tested. The control technology of minimum pollution of overflow can be obtained by comparing the advantages and disadvantages of various control programs, Besides, it can provides a guidance for overflow pollution control in Dianchi Lake Basin.Finally, the study proposes optimal operation mode for pollution control of interception main canal overflow of Dianchi during the rainy season, providing a scientific guidance to further pollution control in Dianchi interception main canal overflow. Specific conclusions of this study include the following:( 1) The sources of pollution of Dianchi Lake interception main canal were investigated and analyzed, and pollutant output and the contribution of each part pollution sources were account. It can be concluded the main pollution source of study area were urban non-point source and non-point source agricultural production.Contaminant transport processes of typical main canal sections were analyzed, at last,targeted pollution of source control strategies were proposed.(2) By analyzing the system structures of Dianchi Lake interception main canal,Interception main canal system dynamic model was established by system dynamics and 8 kinds of overflow pollution control measures for dynamic simulation results were as follows:(1) Source control: Reducing surface runoff coefficient, the runoff at the peak can be reduced by 27%, when the amount of pollution at the peak of the overflow can be reduced by 16%. Thus, the method of controlling effect on surface runoff was better,and also has effect on control of the amount of overflow pollution. Reducing surface runoff pollution load may cause the pollution peak reduction of 55%, and 24%reduction in peak overflow pollution. But obviously this is not a good method to control the amount of sewage overflow.(2) Interception Process Control: Reducing the amount of solids in deposition pipeline during dry weather can reduce 80% of the main canal deposition of pollutants and a 45% reduction of pollution of the overflow at the peak, which indicating that the program for overflow pollution load control has good effect. Construction of storage tank, reducing the amount of water delivered to the pumping station can effectively control the overflow pollution, but large-scale construction of storage tanks has high-cost and need large area. It is needed to according to the actual situation in Dianchi Lake Basin to construct storage tank with appropriate size and number.(3) End pollution control: Interception ratio can be increased from one to three.You can see only a slight reduction in the amount of sewage overflow. It was reduced by approximately 13% at the peak of the runoff, the peak amount of overflow COD reduction amount is only 16%. Compared to the increasing injection of capital and quantity, 16% emission reduction rate was not economical. Increasing terminal equipment to remove suspended solids can remove at the same time about 50% of COD.So increasing the purification devices to reduce pollution of the overflow of the suspension is a feasible method to remove overflow pollution.(4) Overflow pollution control relying solely on a particular measure is not enough.Through simulation of comprehensive measures, the results show that the effect of integrated control is much better than single measure. At last, the minimum overflow pollution control technology program can be determined.(3) Based on scheduling capability analysis of Dianchi Lake interception main cana,and status interception water of interception main canal and water forecast, at last,a kind of integrated optimal operation mode is raised to control overflow pollution in Dianchi during rainy season. By establishing SD model simulation, it is found that taking the middle and end of the accumulator discharge joint scheduling scheduling scheme can maximized closure early rainfall runoff and can provide a theoretical basis and engineering advice to achieve minimized emission of overflow pollution load of interception main canal. |
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