Study On Characteristics Distribution Of Microplastics In Xiamen Urban Wastewater And Its Control Measures

As a new type of marine pollutant,microplastics are easily eaten by marine organisms because of its size,shape and color similar to the food of marine organisms.The self-toxicity of microplastics and the toxic substances adsorbed on its surface have caused direct and potential harm to marine organisms and ecological environment.which has attracted the attention of scholars from all walks of life.At present,the research on microplastics mainly focuses on the distribution and toxicological effects of micro-plastics,However,the research on the sources of microplastics is relatively scarce.The discharge of microplastics from wastewater treatment plants is one of the main sources of marine microplastics,and plays an important role in reducing the discharge of microplastics.Study on the fate of microplastics in wastewater treatment plants can help understand the impact of human activities on the marine environment,and promote the study of sources of microplastics,also can provide a theoretical basis for managing microplastics pollution in municipal wastewater.This paper selects two typical wastewater treatment plants in Xiamen,HaiCang Waterwater Treatment Plant(where industrial and domestic wastewater are separated in influent)and YunDang Wastewater Treatment Plant(where the daily treatment capacity is the largest and there are two kinds of treatment processes at the first stage).Water and sludge are sampled by sampling device,and microplastics in samples are extracted and identified.we study the distribution characteristics of microplastics in wastewater treatment plants,compare the characteristics of microplastics from different wastewater sources and treatment process,and review and analyse a large number of documents and data,have a clearer understanding of the relevant measures to control the pollution of plastics and microplastics at home and abroad bring up some suggestions and measures to reduce the amount of microplastics discharged.The main achievements in this study are as follows:(1)Reveal the distribution characteristics of microplastics in HaiCang and YunDang wastewater treatment plants.The concentration of microplastics in the iffluent of HaiCang and YunDang Wastewater Treatment Plant is 2.026 pieces/L and 1.598 pieces/L,the effluent is 0.142 pieces/L and 0.22 pieces/L the removal rate is 92.99%and 86.23%?The form of microplastics in the two wastewater treatment plants are dominated by fragments,particles and fibers.The colors are dominated by white and transparent.The compositions are dominated by PP and PE.(2)The concentration of microplastics in industrial wastewater of HaiCang wastewater Treatment Plant is 2.764/L,that in domestic wastewater is 1.291/L,and that in industrial wastewater is about twice that in domestic wastewater.There are great differences in form and abundance of microplastics between industrial and domestic wastewater,but there are no obvious differences in particle size and color.Fibrous microplastics in industrial wastewater(43.30%)are higher than domestic wastewater(20.82%).(3)The removal rate of microplastics in secondary treatment process of HaiCang and YunDang Wastewater Treatment Plant is 91.37%and 76.69%,in primary treatment process is 24.25%and 46.56%,the removal rate of microplastics in secondary treatment process is higher than that in primary treatment process;The hydraulic retention time has a great influence on the removal rate of microplastics,and the removal rate increases with the increase of hydraulic retention time;The density of composition of microplastics has a positive correlation with its removal rate.The higher the density of microplastics,the higher the removal rate.(4)In the process of wastewater treatment,microplastics mainly migrate from sewage to sludge through gravity sedimentation and biological scaling,but at the same time,some microplastics reenter the wastewater treatment process through sludge reflux system,forming a closed-circuit cycle of microplastics in wastewater treatment plants.The amount of microplastics(1.35×108)transported into the environment by sludge is much higher than that discharged by sewage(4.69×107)every day.(5)Based on the analysis of the current situation of plastic and microplastics management at home and abroad,bring up the suggestions and measures to reduce the amount of microplastics discharged,It is suggested that industrial microplastics should be the priority control area of microplastics source control of municipal wastewater.