Pollutants Loads Discharged From Point-source In Yixing

Taihu Lake is China's third largest freshwater lake,located in the south wing of the Yangtze River Delta.The Taihu Basin is also one of the highly densely populated areas in China,with its urban and industrial areas.Its unique river network structure provides good water resources for economic and social development in the basin.Statistics in 2018 show that the population of the Taihu Lake Basin accounts for 4.4% of the national population,GDP accounts for 9.8%,and the per capita GDP is 2.2 times that of the country.The acceleration of industrialization and urbanization has caused the Taihu Lake Basin to pay a high consumption and high pollution price.Under the traditional development model of "pollution first,treatment later",most waters have lost their original water supply and ecological functions.In addition,in the process of accelerating urbanization,the rapid increase in the number of immigrants has caused the population density of the Taihu Lake Basin to rise rapidly on the basis of the original level,and the amount of urban domestic sewage has also increased rapidly,leading to a significant reduction in the self-purification capacity of Taihu Lake.Yixing City is located on the west bank of Taihu Lake,and the pollutants produced by it are discharged into the water body to a great extent and affect the water quality of Taihu Lake downstream.However,traditional pollution load calculation cannot accurately characterize the temporal and spatial pattern of regional pollution emissions,and identify the “hot spots” of high pollution load periods and regions,which cannot meet the needs of precise pollution control.Therefore,this study takes industrial point sources in Yixing City and urban residents' living sources as the research objects,combined with field research,accounting for wastewater generated by industrial enterprises and domestic sewage discharged through sewage outlets in residential communities,to build a point source high-resolution spatial information database,Analyze the spatial and temporal distribution of major water pollutants discharged from point sources in Yixing in 2017,and provide a basis for future reduction of water pollutants in Yixing and accurate pollution control of the water environment.According to the calculation results,the following conclusions are obtained:(1)In 2017,Yixing City's point source wastewater discharge amounted to 9292.28 million tons,and the total COD,NH3-N,TN,and TP emissions were 14583.03,2565.5,4792.96,236.96 tons.The discharge of pollutants is higher than that of industrial enterprises.Among them,Qiting Street has the highest discharge of sewage and COD,while NH3-N,TN,and TP have the highest discharge in Dingshu Town.(2)In 2017,Yixing City's industrial point source wastewater discharge totaled 52.822 million tons.From the perspective of the discharge of various industries,the top three wastewater discharges in the year are textile industry,electrical machinery and equipment manufacturing,chemical raw materials and chemical products manufacturing,which discharged 32.185,9.609,29.173 million tons of wastewater respectively.From the perspective of spatial distribution,Qiting Street(Economic and Technological Development Zone)has the most wastewater discharge of 19.2287 million tons;Xinzhuang Street has the least wastewater discharge of 66,500 tons.The emissions of COD,NH3-N,TN and TP are 2642.94,123.15,516.53 and 18.40 tons respectively,and the reduction of COD indicators needs special attention.From the perspective of the emissions of various industries,the discharge of the four types of pollutants is basically the same as the discharge of wastewater.The top three industries in the discharge volume are the textile industry,electrical machinery and equipment manufacturing,chemical raw materials and chemical products manufacturing.The industry with the lowest COD emissions is the agricultural and sideline food processing industry,the NH3-N and TN with the lowest emissions are the metal products industry,and the TP is the chemical fiber manufacturing industry with the lowest emissions.In terms of regional distribution,Qiting Street(Economic and Technological Development Zone)still ranks first among the four types of pollutant discharge.(3)In 2017,a total of 40.104 million tons of wastewater were discharged from urban living sources in Yixing.Among them,the discharge of wastewater on working days was 27.493 million tons,and the discharge on rest days was 12.64 million tons.Judging from the discharge of townships and streets,the sewage discharge per unit area in densely populated areas is relatively high.The top three areas are Yicheng Street,Qiting Street,and Dingshu Town.The COD,NH3-N,TN,and TP emissions from urban living sources were 11958.09,2442.35,4276.43,and 21.856 tons respectively.The area with the highest emission of the four types of pollutants is Ding Shu Town,Yicheng Street,Gaocheng Town,and Heqiao Town are also areas that need special attention for pollution control.Based on the above accounting results,this study proposes the following countermeasures and suggestions from the perspective of pollution control:(1)Combining the actual situation of Yixing City,shut down some high-pollution enterprises,promote business mergers,and eliminate backward technology and production capacity;(2)Strengthen the life of densely populated areas At the same time of sewage collection and treatment,the management of pollutant discharge in rural areas cannot be ignored;(3)Establish and improve a data information sharing platform to provide conditions for precise pollution control in Yixing City.