Study On Permissible Load Calculation And Pollution Load Reduction Program Assessment Of Wujin River Watershed Based On Water Quality Model

With the development of social and economic, China’s water environment pollution problems have become increasingly prominent, so scientific and effective studies on water pollution total amount control and load reduction are urgent to carry out. At present, the pollutant total amount control that based on the water environment capacity is the development trend of water pollution control, and the basin is the most effective water pollution control unit. Therefore, study on the basin pollutant permissible load and load reduction has important theoretical and practical significance.In this study, Wujin River watershed which located in Jiangsu Province are selected as study object, the major pollution sources and water quality excessive factor of the Wujin River watershed are determined by the pollution sources estimation and water quality assessment, the water quality model of Wujin River was established use QUAL2K model and it was calibrated and validated. Permissible load of the Wujin River watershed was calculated by trial and error method, water pollutant emission total amount control strategies and measures of Wujin River watershed were proposed, five types of watershed load reduction programs were simulated and evaluated. Finally, the method of optimizing and selecting of river water quality improvement programs was provided. The main research contents and results include the following aspects:(1) The water qualities of Wujin River were evaluated using the single factor index method to determine the water quality factors which should be simulated.The water quality monitoring data of Wujin River’s major water quality monitoring sections in2010were evaluated using the single factor index method. Key water quality factors including COD, NH3-N, TN and TP were exceeded, so these four water quality factors were selected to conduct the water quality modeling and water environmental capacity calculation.(2) Divided the reach of Wujin River and determined the methods of inputting model data by QUAL2K water quality model, established the Wujin River water quality model through model calibration and validation.Main stream of Wujin River is35km, divided into eight reach. Wujin River water quality monitoring data of dry period, normal period, wet period and the annual average in2010were used for the calibration of model parameters, respectively, COD oxidation rate, ammonium nitrification rate, nitrate denitrification rate, organic N hydrolysis rate, organic P hydrolysis rate, and inorganic P settling velocity rate of dry period, normal period, wet period and the annual average were obtained, respectively. The Wujin River average annual water quality monitoring data in2011were used for the verification of model parameters, the results show that the simulated values of Wujin River water quality modeling and measured values are in good agreement, indicating that the model has good simulation accuracy and it can be well quantitative description the time and spatial changes in water quality of Wujin River.(3) The permissible load of Wujin River main stream in different water periods were calculated by trial and error method.Combined with the actual location of the pollution sources in Wujin River watershed, permissible load were calculated using trial and error method, of the COD, water environmental capacity of ammonia nitrogen, total nitrogen and total phosphorus of each reach in different water periods were obtained. Water environment capacities of Wujin River are largest in upstream, followed by midstream and downstream.(4) The related measures of pollutant emission total amount control in Wujin River watershed were proposed.According to the pollution load emissions of the Wujin River watershed, which compared the simulation results of permissible load, the pollution load reductions of all reaches were calculated, found that the water environmental capacity of upstream is serious shortage. The major countermeasures of water pollutant total amount control in Wujin River watershed were proposed based on the watershed actual situation, which including the reduction ratio of river pollution load, the various measures of water pollutant source control, as well as the economic and management measures of total amount control, the pollution control technologies of riverway were proposed intensively.(5) Five types of pollution load reduction programs were simulated and evaluated.A variety of pollution load reduction programs were designed, including the five types:①Control point sources and non-point sources;②Only control the point sources;③Only control the non-point sources;④Only control the rives;⑤Control point sources, non-point sources and rivers. The load reduction rate of various programs required while the water quality of the river end meet the standards were obtained. As the evaluation results showed, both control the pollution source and governant the polluted river have the operability and usability.(6) Optimization and selection of river water quality improvement programs.The Hongqi River in Wujin River watershed was selected as case study, six different water quality improvement programs which designed from combinations of three water treatment techniques, including vertical moveable eco-bed technology, bio-contact oxidation technology, and ecological floating bed technology were simulated by QUAL2K. Through comprehensive evaluation, the optimal program for the Hongqi River comprised a bio-contact oxidation system in the upper river, an ecological floating bed in the middle river, and a vertical moveable eco-bed in the lower river.