Research On The Distribution Characteristics Of Microplastics In Municipal Wastewater Treatment Plants And The Adsorption Of Microplastics On Heavy Metals

Microplastics refer to plastic particles with a particle size of less than 5mm.As a new type of pollutant,it has attracted much attention in recent years.Some research shows that wastewater treatment plants play an important role in releasing microplastics into the environment.There,effective detection of microplastics and understanding the migration and fate of microplastics in wastewater treatment plant are of great significance to the control of microplastcis pollution.Heavy metals pollution has also attracted much attention in recent years.As a potential carrier of pollutants,microplastics can adsorb heavy metals in aquatic environments due to their high hydrophobicity and specific surface area.This research uses microplastics and heavy metal as the starting point to study the distribution characteristics of microplastics in wastewater treatment plants and the adsorption behavior of microplastics on heavy metals.In this study,we first selected Xiamen Jimei Wastewater Treatment Plant as the research object and investigate the distribution characteristics of microplastics in Jimei Wastewater Treatment Plant,and compare the difference in the removal of microplastics by different secondary treatment.In addition,the adsorption behavior of polyamide(PA),polyvinyl(PVC)and polyethylene(PE)to lead,nickel and zinc was investigated.The main results in this paper are as follows:(1)The concentration of microplastics in the influent of Jimei wastewater treatment plant is 4.26 pieces/L,the effluent of cyclone grit chamber is 2.82 pieces/L,the effluent of oxidation ditch is 1.62 pieces/L,the effluent of anaerobic anoxic oxic is 1.85 pieces/L,the effluent of Jimei Wastewater treatment plant is 0.56 pieces/L.The color of microplastics in the wastewater treatment plant are dominated by white and transparent,the shape are dominated by fragments and fibers,the main type of microplastics are PA,PE and PP.The removal rate of microlplastics in the swirl grit chamber is 33.8%.By comparing the difference in the removal efficiency of microplastics between the oxidation ditch and anaerobic anoxic oxic found that the removal rate of the microplastics is 55.6%and 61.9%,respectively.(2)The scanning electron microscope(SEM)shows that the surface of PA has more pore structure compare with PVC and PE.X-ray Photoelectron Spectroscopy shows that the chemical bond of three microplastics is the same with chemical formula.Adsorption experiments are developed at the temperature of 20℃,25℃ and 30℃,the concentrations of humic acid is 0、10、20、50mg/L,respectively,the initial concentrations of heavy metals at 5 mg/L and the amount of microplastics at 20 g/L.The adsorption capacity of PA to heavy metals is decrease with increase of temperature,while PVC and PE are opposite.The adsorption capacity order of three microplastics to heavy metals is PA>PVC>PE.Humic acid can enhance the adsorption of microplastics to heavy metals.