Occurrence Of Microplastics In Wastewater Treatment Plants And Characteristics Of The Microsphere

Microplastics(plastics with a particle size of less than 5mm),because of their small size,light weight,and easy diffusion,are widely stored in various environmental media,attracting great attention from their scholars.Recent studies have shown that microplastics can be used as a carrier for microbial attachment,just like natural substrates.The research on the interaction between this special ecological niche and the microplastic microbial community has special environmental significance.Sewage treatment plants are an important way for microplastics to enter the environment.As a new ecological niche,microplastics can provide new colonization space for microorganisms.Microplastics may eventually be discharged into environmental water bodies through sewage treatment plants carrying microorganisms.In order to understand the discharge of microplastics and the load of biofilms in sewage treatment plants,this study first took four sewage treatment plants in a large city as an example,and investigated the occurrence characteristics of microplastics in the inflow and outflow of the four sewage plants.The abundances were 23.32-31.50n/L,and the average emission flux was 1.45×10~7 n/d.The main type of microplastics is PA.Based on the above investigation,the main microplastic type PA was selected as the research object,and the effect of biofilm formation under in-situ cultivation in each treatment unit of the sewage treatment plant was explored.Specifically include:analysis of the characteristics of the biofilm on the plastic surface,such as the total amount of biofilm on the PA film surface in each treatment unit of the sewage treatment plant,the density of the biofilm,the three-dimensional structure,the microscopic morphology and other basic characteristics,and the release of extracellular polymers from the biofilm;In addition,the impact of biofilm on the physical and chemical properties of microplastics is explored,such as the impact of biofilms on the roughness,functional groups and crystal structure of PA;finally,the community succession characteristics of microplastics in biofilms are investigated,and different treatments are investigated through metagenomic sequencing.The changes in the structural characteristics of the microbial community of the unit environment and the surface biofilm of PA and when the PA migrates in different treatment units of the sewage treatment plant.The research results show that there are differences in the surface growth of microplastics and the morphology of biofilms between the processing units.The changes of proteins and polysaccharides in the extracellular polymer of the biofilm on the surface of the microplastics in each processing unit basically change simultaneously,and the protein content is significantly higher than the polysaccharide content.The formation of biofilm on the surface of microplastics has a limited effect on the composition of functional groups and crystallinity of microplastics.The species composition of the biofilm on the microplastic surface is obviously different from that of the culture water.Different species have different colonization ability on plastic surfaces,and Pseudomonas can colonize the microplastic surface preferentially.When the plastic circle sample is transferred from the upstream culture unit to the downstream culture unit and the culture environment changes,the microbial composition of the biofilm on the surface of the plastic circle sample is closer to that of the downstream culture unit,but there is still a certain difference from the plastic circle sample that is continuously cultured in this unit.