Distribution,Source And Risk Assessment Of Microplastics In Urban Natural Water And Sewerage System

Microplastics（MPs）pollution is one of the most important concerns in the global water security field,and it has become one of the most important environmental problems on par with climate change.China is the largest producer of plastics in the world.In recent years,with the further expansion of the production,unreasonable use and inefficient management of plastic products in China,the existing monitoring data show that MPs pollution has been widely distributed in various rivers,lakes,Marine waters,land and other environments in China,resulting in huge environmental and ecological risks.Cities are the main source of MPs pollution,and the research on the output of MPs pollution is the key to MPs pollution control.As a megalopolis,Shanghai is the central city of the Yangtze river delta urban agglomeration and the largest financial city in China.At the same time,Shanghai is located in the alluvial plain of the Yangtze river delta,connecting the large high-density population aggregation area with the river network of the Taihu lake basin and the estuary coast of the Yangtze river delta.It is a typical area where MPs pollution occurs and migrates.The MPs pollution risk is severe,which is of great significance for the study of MPs pollution in Shanghai.However,at present,the awareness of this problem and related monitoring are still insufficient,and systematic and comprehensive census and targeted risk assessment have not been carried out according to the geographical environment and human activity characteristics of the region.Therefore,it is difficult to put forward the key technologies,policies and measures of MPs pollution prevention and control more effectively.Therefore,this research in view of urban drinking water source,main channel and the water system,mainly is the rainy season put jiang and sewage treatment plant,the pump based on MPs concentration,type,particle size distribution characteristics and the related characterization of parsing the sources of the MPs in all kinds of city water body and the environment factor,correlation,and different types of drainage pump station during the rainy season discharge MPs dynamic value and its influence on river MPs.At the same time,the removal efficiency and trend of MPs in various treatment processes of municipal sewage treatment plants are clarified.On this basis,the MPs pollution risk entropy assessment method system was established,and the MPs pollution risk assessment was carried out for urban natural water bodies and sewage systems.This study can clarify the distribution of MPs in urban natural water bodies and sewage systems,trace the source of MPs in urban water bodies,and provide references for the control of MPs in the later stage.At the same time,the establishment of MPs risk assessment method provides a basis for quantifying the ecological risks caused by MPs in water.The main conclusions of this study are as follows:（1）The concentration of MPs in Suzhou River,Huangpu River and Jinze Water Source was14.39±5.14 P·L^-1,26.21±9.63 P·L^-1 and 28.28±4.06 P·L^-1,respectively.The concentration of MPs in Suzhou River sediments was 6233.38±1890.40 P·kg^-1.In general,the type of MPs is mainly PET,the shape is linear,the color is colorless and transparent,and the proportion of small particle size（80～500μm）is the largest.（2）The discharge process of the pump station will release a large number of MPs into the water.The pumping station will release a large amount of MPs into the water body during the process of releasing the river.The average concentration of MPs in the pumping station and channel outlet of Furongjiang Pumping Station were 4337.78±2703.12 P·L^-1 and 4623.78±2855.11 P·L^-1 respectively.The average concentration of MPs in internal and river outlets of Huayang Pumping Station were1965.56±819.23 P·L^-1 and 1221.11±437.71 P·L^-1 respectively.The average concentration of MPs in the pumping station and channel outlet of Yichang Pumping Station were 3137.00±1371.54 P·L^-1and 1955.25±1025.17 P·L^-1 respectively.The average concentration of MPs in the pumping station and channel outlet of Guangyu Pumping Station is 1804.29±817.56 P·L^-1 and 1535.71±346.30 P·L^-1respectively.The average concentration of MPs in the pumping station and channel of Chengdubei Pumping Station were 3158.00±2328.55 P·L^-1 and 2347.00±974.97 P·L^-1 respectively.The average concentration of MPs in the pumping station and channel of Fujianzhong Pumping Station were949±447.83 P·L^-1 and 1581±511.18 P·L^-1,respectively.PET is the main type of MPs in the discharge process of the pump station.The interior of the pump station accounts for the largest proportion of granular MPs,and the linear MPs at the river outlet accounts for the largest proportion.The MPs concentration in the discharge process of pump station is related to the rainfall process,and the change rule of MPs in the discharge process of pump station with time is basically consistent with the rainfall intensity.According to the statistical data calculated by the drainage company and Shanghai statistical yearbook 2017,the annual displacement of MPs in 42 pumping stations along Suzhou river is about 0.99×10¹⁴ P·year^-1,while the annual displacement of MPs in 56 sewage treatment plants in Shanghai is 1.39×10¹⁴ P·year^-1.（3）The wastewater treatment plants contain a large number of MPs,and the average concentration of influent MPs is 199.8±27.19 P·L^-1.The types are mainly PET（polyethylene terephthalate）,PA（Polyamide）,PE（polyethylene）and PP（Polypropylene）,and the removal efficiency of MPs is about 60%.The removal rate of MPs in the two primary treatment processes accounts for 70%～80%of the total treatment process.The regression trend of MPs in sewage treatment plants was calculated,and it was shown that 38.82%±1.55%MPs entered the receiving water body with the effluent,and the remaining 61.18%±1.55%MPs entered the excess sludge.（4）PCA statistics based on MPs and general index data of sampling points show that domestic source is the main source of MPs in Suzhou river.The source of MPs in Huangpu river is complex,and MPs in water are mainly affected by different types of land use.In addition,atmospheric deposition is also a factor affecting MPs in urban watercourses,especially in Huangpu river.（5）Based on the MPs risk entropy risk assessment method system,the data show that MPs in urban natural water does not constitute ecological risk,and the effluent from urban sewage treatment plant does not form ecological risk.But pumping station overflows pose significant ecological risks.Moreover,the dynamic change of ecological risk is consistent with the hydrodynamic change process of overflow,and the risk degree of different pump stations is different.