Occurrence Of Microplastics In Rivers And Sewage Plants In Inland Cities

As a new type of environmental pollutants,microplastics have attracted widespread attention in the international community because of their small size and easy adsorption of pollutants in the environment,and they are easily swallowed by organisms in water bodies.At present,research on microplastics is mostly concentrated in the marine environment,but there are few reports in the freshwater environment with frequent human activities,which needs to be further enriched and improved.In this dissertation,the rivers in the urban section of the Bahe River and two typical urban sewage treatment plants are selected as research objects.Micro-plastic detection methods in freshwater environments are determined using experimental simulation of microplastic separation and extraction processes.The microplastics pollution in mud was studied;the relationship between the microplastics occurrence characteristics and the removal rate of microplastics in different treatment processes was compared and analyzed;based on the literature,a model for analyzing microplastics sources in specific areas was proposed and introduced.Diversity index to show the distribution characteristics of microplastics in freshwater environment.(1)By investigating the pollution characteristics of microplastics in the water bodies of eight stations in the urban section of Bahe and Xi'an's third and fifth sewage plants,it was found that the abundance of microplastics in river waters,with an average of 6.53±2.36 to 36.13±14.03 particles per /L,the main types of microplastics are fibers and debris,of which the proportion of fibers in water is(90.98±9.26)%,foaming microplastics are only present in water samples;the amount of microplastics in the wastewater of Xi'an Third Sewage Plant It is 57.45±5.5 particles per /L,the effluent is 6.5±0.73 particles per /L,the total removal rate of microplastics is 88.69%;the number of microplastics in the influent of the fifth sewage plant is 17.05±3.38 particles per /L,the effluent is 4.57±0.71 particles per /L,the total removal rate of microplastics was 73.2%.The results show that different sources of wastewater are the main reasons affecting the abundance of microplastics,while conventional wastewater treatment processes cannot remove microplastics in wastewater well,and a physical retention process needs to be added for improvement.(2)The distribution characteristics of microplastics in river sediments and sewage sludge were analyzed,and it was found that the abundance of microplastics in river sediments was 9.52-25.06 particles per gram of dry sludge,and 68.46±3.31?214.67±19.12 particles per gram in the sewage sludge.The main types of microplastics are fibers and debris.There is no obviously discrepancy in the size distribution of microplastics in water samples and sediments,and the small size microplastics in water samples dominate,which proves that microplastics break with migration.(3)Establish a micro-plastic source analysis model in a specific functional area,analyze and summarize the micro-plastic sources in the river,and find that they mainly come from secondary micro-plastics produced by domestic sewage discharge,industrial waste,fishing activities,and human activities.After introducing the concept of microplastics diversity index,it was found that the characteristics of microplastics pollution in different functional areas of rivers were different through calculation and analysis.By investigating the occurrence of microplastics in rivers and sewage plants in inland cities,the level of microplastics pollution in inland areas is clarified and provided basic data for the similar inland cities;the analysis model of microplastics sources in specific functional areas can conveniently determine the source of microplastics,and then propose treatment methods.