Study On The Behavior Of Microplastics Leaching Dissolved Organic Matter During The Chlorination Disinfection And The Generation Risk Of Disinfection By-products

In recent years,the emergence of microplastics has increasingly become a major environmental challenge in drinking water systems.Although the potential effects of microplastics in drinking water on the human body are not well understood,MPs come to public attention when they are introduced into the human body through drinking water.Current drinking-water treatment plant structures are an important safeguard against microplastics.Therefore,it is very important to understand the removal efficiency of microplastics in each link of water purification plant.At present,there is no research on the chlorination process of microplastics.This topic selected two common MPs in drinking water sources-polypropylene(PP)and polystyrene(PS)as the research object.First,characterize the MPs after chlorination disinfection.According to the chlorination process,the leaching of dissolved organic matter and the disinfection by-products generated by MPs were studied.The leaching of dissolved organic matter by MPs under different particle sizes,different types,and different initial chlorine dosages was studied.The possible mechanism of action of the chlorination disinfection process on MPs is proposed.And analyzed the interaction between MPs and disinfection by-products.The following conclusions were obtained:(1)The physical and chemical properties of MPs before and after chlorination have certain changes.The color of the chlorinated MPs turns yellow.The PP surface has wrinkles,and the PS surface has obvious cracks.The contact angle of MPs after chlorination has been significantly reduced,and decreases with the increase of the initial chlorine dosage.The decrease of the contact angle increases the surface polarity of MPs and weakens the hydrophobicity.Obvious oxygen-containing functional groups appeared on the infrared spectrum and EDS energy spectrum of MPs after chlorination.Its CI value and O/C ratio both increase,PS found the formation of chlorine in the EDS test,It can be speculated that the main reactions of chlorination to MPs are chlorination and oxidation.(2)MPs will leach soluble organic matter in water,and the leaching concentration will be affected by the particle size and type of MPs.The leaching amount of small particle size is slightly higher than that of large particle size,and the leaching amount of PS is higher than that of PP.After chlorination,the concentration of MP-DOC first increases,then decreases,and finally stabilizes.Generally speaking,the dissolved organic matter leached on the 7th day was higher than that without chlorine addition,and it increased with the increase of the initial chlorine dosage.When the dosage of chlorine is >8 mg/L,the PS-DOC concentration will have a peak effect on the next day.The molecular characteristics of the dissolved organic matter leached out the second day after PS was chlorinated were investigated,and it was found that the products were mainly phenolic substances with small molecular weight and fluorescence.The decrease in fluorescence on the third day may be due to the re-adsorption of the produced substances by MPs.(3)Only trichloromethane was detected in the trihalomethanes produced by MPs.The chlorination reaction of MPs leaching solution was carried out for 7 days,and the disinfection by-products produced were related to the DOC concentration,that is,to the particle size and the types of MPs.The generation potential of MPs disinfection byproducts has a greater health risk than natural organic matter and algae organic matter.The presence of MPs will affect the generation of disinfection by-products,which will increase the consumption of chlorine and reduce the generation of disinfection byproducts.The decrease in residual chlorine is due to the reaction of a part of the chlorine with MPs,resulting in an increase in chlorine consumption.MPs adsorbs chloroform,resulting in a decrease in the concentration of disinfection byproducts.(4)MPs particle size,type,and chlorination oxidation all affect the adsorption of MPs on chloroform.The smaller the particle size,the stronger the adsorption capacity of MPs.Compared with PP,the adsorption capacity of PS is stronger.MPs without chlorination and oxidation have stronger adsorption of chloroform than chlorinated MPs.The adsorption behavior of MPs on chloroform will be affected by many factors.There is a dynamic process of adsorption and desorption between MPs and chloroform in the chlorination process.The conclusions of this study can be used to analyze the changes of MPs in chlorination disinfection and their leaching behavior of dissolved organic matter,and to explore the health risks of MPs during the chlorination disinfection process.Through the study of chlorination and disinfection of MPs,it provides optimized parameters and theoretical basis for the efficient removal of MPs in water,and effectively guarantees the safety of water quality.