Comparative Study On Distribution And Trend Of Microplastics In Wastewater Treatment Plants With Different Processes

At present,microplastics has become a serious pollutant ubiquitous in surface water,seawater and soil,which has a serious impact on the ecosystem and aroused widespread concern around the world.Sewage treatment plant is considered as the main purification link of land microplastics entering natural aquatic system.Therefore,studying how to improve the microplastics removal capacity of sewage treatment plant will become an indispensable part to solve the pollution problem in microplastics.In this study,four representative sewage treatment plants in Zhenjiang were selected for sampling study,and the microplastics in sewage and sludge was detected.The abundance and characteristic composition of microplastics in the process flow were studied,and the differences of microplastics after different sewage treatment scales,regional characteristics and different treatment processes were compared.The main conclusions are as follows:(1)A total of 14 kinds of microplastics were detected by microplastics Raman detection and analysis of water samples from various sewage plants,among which PE accounted for about 40%,PP,PS and PET accounted for 5%-40%,and plastics such as PA,PC,POM and PMMA accounted for a relatively low proportion.The occurrence of microplastics in sewage plants is mainly fibrous,followed by particles and irregular shapes;Microplastics of 20-100μm is mostly,accounting for about 80%;Most of the colors are colored and transparent.(2)The cyclone grit chamber in primary treatment is helpful to remove microplastics,and the removal effect of microplastics in secondary treatment is uct >A2/O > biolak.The removal rate of fiber microplastics by secondary treatment is higher(87.4%-91%).After primary and secondary treatment,the removal rate of microplastics larger than 500μm can reach 100%;The removal rate of color and black microplastics is over 70% in the secondary treatment process.The distribution of microplastics in sludge is basically the same as that in sewage,and the abundance of microplastics in secondary sludge is obviously higher than that in primary sludge and dry sludge.In addition,there are many internal circulation flows in the sewage treatment plant in microplastics,and most of them are enriched in the secondary treatment sludge,and finally the sludge is dried into mud cakes which are imported into the environment from the sewage treatment plant.(3)The larger the scale,the higher the quantity of microplastics carried by sewage.The better the sedimentation performance of sludge,the better the removal rate of microplasticity.The increase of hydraulic retention time reduces the flow and turnover rate of sewage and is helpful to the removal of microplastics;Increasing sludge load can increase wastewater treatment capacity to a certain extent,thus improving the removal effect of microplastics.In the future,the removal of microplastics in sewage treatment plants can be promoted by improving the interception of microplastics by primary treatment and improving the biochemical action in activated sludge;In addition,increasing the purification of backwater generated during sludge dewatering and improving sludge disposal methods will help to reduce the microplastics in sludge entering the soil environment.