The Water Quality Improvement Of Lake Regions Caused By The Interception Of Sewage Project In The South Lake

With the development of society and economy in China, the water consumption and sewage emission of the city increase rapidly, a large amount of sewage is discharged into the water body directly, which greatly pollutes the lake water body. The South Lake is a very big closed lake. Because the sewage is discharged into the lake in long-term, it has already lost the basic function of water body. It is necessary to investigate the outlets actuality and the water quality transformation reguality of the South Lake.The investigation results of outlets indicate that there are forty-three sewage outlets around the South Lake. About 164,000 tons sewage is discharged into the South Lake, among them nearly 150,000 tons sewage enter into the small South Lake and nearly 14,000 tons sewage enter into the big South Lake everyday directly. The sewage quality characteristics of most outlets is similar to municipal sewage of Wuhan, the concentration of organic matter is very low. The concentration of CODCr, TN, TP is relatively high, which cause the serious pollution in South Lake.The outlet's sewage is a main point pollution source.The first part of this study is to investigate and monitor the pollution situation of water quality of water substances in South Lake, and the draining situation of drain outlets. The quantity and pollutant burden of sewage that drained into South Lake by drain outlets can be measured. After the quantitative analysis on the point source pollution in South Lake, the period study can be provided for the comprehensive treatment to stop pollution or after pollution. The self-purification rules of pollutants in the drain outlets are analyzed, and water quality model is built to simulate and calculate the distribution of concentration field of pollutants in water area round the drain outlets. Those provide a theoretical foundation to analyze the rules of concentration changes of pollutants in the South Lake. The Longwangzui wastewater treatment plant outlet is a bigger sewage outlet of the South Lake, the amount of sewage is more than 150000 tons everyday. The Water quality model of water body near the Longwangzui wastewater treatment plant is based on the sewage characteristic analysis. The treated water pollutants are divided into two parts:settled matter and unsettled matter. The self-purification of settled matter in the water body is sedimentation and the unsettled's is diffusion by laminar flow and dilution by turbulence flow. The two parts enter into lake and mix with the water in lake altogether. The comprehensive self-purification coefficient of CODCr,TN and TP are deduced by the water quality monitor data near the outlet and the coefficient of CODCr,TN and TP is 362.88d-1,362.88d-1,152.91 d-1 each.The second part of this study concerns the water quality improvement of lake region caused by the interception of sewage project in the South Lake should consider the influence to the South Lake water quality made by different pollution sources. And it built the sewage collection system for the sewage around South Lake, at the same time it built the Longwangzui waste water treatment plant and the Rongjun pumping station. All of these provide good condition for the interception of the pollutant discharging outlets around the South Lake.To know the improvement of the South Lake water quality after the interception of sewage, it is very necessary to analyze the present situation of self-purification contents in the South Lake. To accurately analyze the self-purification contents of water body, at first we need to set up the interrelation model of the pollutants and water body, and then we can analyze the migration transformation rule of the pollutants in the water body. According to the investigations about the South Lake water body and the environment nearby, we can set up the migration transformation model of the pollutants in the South Lake water bodyAccording the migration transformation model of the pollutants in the South Lake water body, divides the pollutant migration into six parts:point source(pollutant discharging outlet), the area source (atmosphere rainfall, fall dust), inner source (the bottom mud release), fishery cultivation, the regulating and storing, water body self-purification. The self-purification coefficient K'C, K'N and K'P of the South Lake water body is 0.0245 d-1,0.0132 d-1,0.0754 d-1However, with the rapid development of the regional economy around the South Lake, the recent situation of the water drainage in this area and the South Lake are all changing constantly, and the drainage plan of the whole South Lake area is doing adjustment according to the changes. Therefore, the interception of sewage in the South Lake should do some adjustment and improvement according to the actual conditions urgently.