The Analysis Of Microplastics’ Distribution In Wastewater Treatment Plants And It’s Adsorption To Tetracycline And Copper

The widespread use of plastics in the world has caused serious environmental pollution problems.Microplastics（MPs）that were broken and decomposed in the environment migrate with water or the atmosphere,causing a series of hazards and being considered as a new class of environmental pollutants.Wastewater treatment plants（WWTPs）were important source of MPs.It is important to understand the distribution of MPs in the main process units of WWTPs.MPs have a certain adsorbability to environmental pollutants.The adsorption behavior of microplastics and harmful pollutants in the presence of them remains to be determined.This study selected the two WWTPs in Chengdu,analyzed the presence of MPs.Taking polystyrene（PS）MPs（Which were widely exists in the WWTPs）as the research object,the adsorption behavior of tetracycline（TC）and copper（Cu）in water environment was simulatedand,the influence of pH,salinity and dissolved organic matter（DOM）contents on the adsorption performance of PS were also studied.Aimed at:（1）To explore the distribution of MPs in each treatment link of WWTPs;（2）The adsorption behavior and influencing factors of heavy metal Cu and TC on PS with different particle sizes were revealed by laboratory simulation adsorption;（3）To investigate the effects of ultraviolet aging on the surface properties of PS and the adsorption differences and behaviors of heavy metals Cu and TC of PS after aging.The results of this paper provide a theoretical reference for clarifying the distribution of microplastics in WWTPs and the ecological risks after their interactions with pollutants.The main conclusions are as follows:（1）MPs were detected in the sludge of each process unit of the WWTPs.The overall abundance of MPs is 44.44-750 n·kg^-1.MPs are mainly divided into particles（32.16%）,fragments（28.14%）and fibers（17.08%）according to their shapes.The color basically has green（35.19%）,translucent（18.06%）,white（16.67%）,red（16.20%）;The particle size was mainly larger than 1 mm in diameter,accounting for 68.35%.The larger the particle size,the easier the microplastics were removed.MPs components are mainly polyethylene,polypropylene and polystyrene.（2）The smaller the particle size,the higher the specific surface area and the larger the adsorption capacity of PS.The adsorption process of TC involves hydrophobic interactions and other interactions（such as electrostatic andπ-πinteractions）.The adsorption of Cu ions by single layer is dominated by electrostatic interaction.pH had obvious effect on the adsorption,the presence of dissolved organic matter inhibited the adsorption,and salinity had limited effect on the adsorption of tetracycline on microplastics.（3）Under ultraviolet aging,the hydrophobicity of PS decreases with the growth of aging time.Aging reduces the crystallinity of the material,produces tiny cracks on the surface,and produces new oxygen-containing functional groups under photooxidation,resulting in reduced hydrophobicity.The longer the aging time is,the adsorption amount of TC and Cu on PS increases,and the adsorption is dominated by ion exchange adsorption.On the heterogeneous surface,the aging PS show the trend of multi-layer adsorption.pH and salinity play important roles in adsorption.In summary,The composition of microplastics in sewage sludge is complex,and the abundance is large.In the environment,particle size changes caused by mechanical wear and aging caused by photooxidation will bring physical and chemical changes to the surface of MPs,so it can absorb more TC and Cu.