The Influence And Mechanism Of Microplastics On The Removal Of PPCPs By Typical Advanced Oxidation Processes

Microplastics and pharmaceuticals and personal care products（PPCPs）are two emerging pollutants that coexist for a long time in the aquatic environment.Microplastics can significantly affect the migration and transformation behavior of PPCPs in the aquatic environment.However,advanced oxidation processes（AOPs）for water pollution focus on removing PPCPs,and there is still a lack of comprehensive understanding of the changes and mechanisms of PPCPs removal by AOPs when microplastics coexist.The research on AOPs removal does not match the current complex pollutants in the aquatic environment.This study investigated the adsorption of coexisting PPCPs on microplastics and analyzed the characteristics of the aged microplastics and their effects on the adsorption of PPCPs.The roles of microplastics in adsorption and enrichment of organic pollutants,consumption of active free radicals,and hindering the mass transfer of oxidizing species were clarified during Fenton,ferrate,and electro-peroxone processes.The influence and mechanism of microplastics on the removal of PPCPs by typical AOPs were revealed based on experimental results and simulations.The main findings of this study are listed as follows:（i）Study on adsorption mechanism.The specific surface area,total pore volume,carbonyl index,and O and N contents of the short-term aged polypropylene increased.The initial adsorption rates（0.123–1.832mg/（g min））and equilibrium adsorption capacities（q_e,0.332–2.558 mg/g）of 12 PPCPs on aged polypropylene were higher than those of polypropylene（0.047–0.624 mg/（g min）and 0.125–1.448 mg/g）.Adsorption kinetics and isotherm models indicated that the liquid-film and intra-particle diffusion affected the adsorption of PPCPs on the aged polypropylene,while the surface diffusion was a rate-limiting step for polypropylene.The linear free energy relationship and structural activity models revealed that hydrophobicity and hydrogen bonding interaction dominated the adsorption of PPCPs on polypropylene,and electrostatic interaction and hydrogen bonding controlled the adsorption of PPCPs on aged polypropylene.（ii）Construction of adsorption capacity prediction model.The total q_e of 66 PPCPs on 15 unaged microplastics was 0.172–1.044 mg/g,much lower than that of 177 long-term aged microplastics（7.114–13.114mg/g）.Taking the structural parameters of PPCPs and the infrared spectral transmittance of microplastics at 650-4000 cm^-1 as independent variables,the maximum information coefficient-gradient boosting decision algorithm was used to build machine learning prediction models for predicting q_e of mixed PPCPs on microplastics.R_training² of the two models was over 0.977,and R_test² was over 0.740,suggesting that the model had excellent predictive and generalization abilities.Model analysis showed that q_e of mixed PPCPs on 134 microplastics was related to its calculated energy under B3LYP/6-31G*;on the surface of microplastics,functional groups with absorption in the wavelength range of 734–974 cm^-1,1292–1448cm^-1,1510–1524 cm^-1,1586–1692 cm^-1,and 2980–3332 cm^-1 exhibited more significant impacts on q_e,and the carbon skeleton and C=O were the primary functional groups.（iii）Influence and mechanism of microplastics in the Fenton process.The inhibition rate of polypropylene was 1.19%–2.10%,which was lower than that of the other 11 aged polypropylene（11.17%–75.67%）,and H₂SO₄ aged polypropylene had a promoting ratio of 9.08%.Electron spin resonance results showed that the presence of polypropylene consumed hydroxyl radicals（HO·）.In addition,the fluorescence signal and total organic carbon of the solution implied that polypropylene increased the fluorescence signal of the system solution after treatment to increase the response area of small soluble molecules,and the response intensity increased by 500 a.u.The total organic carbon increased by 20%.The relative proportions of C=O and C-O on its surface increased to 1.5%and5.3%,respectively.Moreover,the carbonyl index increased to 1.82.Polypropylene was undergoing aging,and small soluble molecules were released during the Fenton process.Meanwhile,polypropylene’s surface S and Fe increased to 4.29%and 1.81%,respectively,which confirmed that polypropylene could also adsorb SAs and its derivatives and catalyst Fe ions.（iv）Influence and mechanism of microplastics in the ferrate process.Original polystyrene and H₂SO₄,Na OH,and Fenton aged polystyrene promoted the removal of three tetracyclines by ferrate.Due to the coagulation of Fe³⁺in the ferrate process,the particle size and density of microplastics affected the removal of TCs by affecting their coagulation,the promotion rate was more significant than 21.0%,but the small particles（180-250μm）and high density（greater than 1.0 g/cm³）showed a slight inhibition.Fluorescence response intensity increased by 280 a.u.,and total organic carbon increased by 7.4%.The surface of polystyrene increased-OH,carbonyl index increased slightly to 1.68,indicating that in the Fe VI process,polystyrene experienced slight aging and small molecules were released;Meanwhile,the relative content of Cl and Fe on the surface of polystyrene increased to 0.16%and 0.51%,indicating that polystyrene adsorbed tetracyclines and their derivatives,and Fe（OH）₃,and they were removed by coagulation.（v）Influence and mechanism of microplastics in the electro-peroxone process.Microplastics reduced the HO·concentration at the electrochemical cathode/solution interface.However,they exhibited no significant effect on the concentration and diffusion path of gaseous O₃ at the device inlet and H₂O₂ on the electrochemical cathode surface,indicating that microplastics adhering to the cathode surface would inhibit the diffusion of HO·from the electrochemical cathode surface into the solution,thereby reducing the removal ratio of PPCPs.The average particle size of microplastics increased from 135.0μm to 750μm,and the average turbulent kinetic energy and turbulent dissipation rate increased by 0.027 k m²/s² and 0.041 m²/s³,respectively;the number of microplastics particles increased from 3737 to 5462（500 m L solution）,the average turbulent kinetic energy and turbulent dissipation rate increased by 0.018 k m²/s² and0.702 m²/s³,respectively.It showed that increasing the particle size and the number of microplastics hindered the flow of the solution,weakened the conversion efficiency of gas-phase O₃ to liquid-phase O₃ in the EP process,and reduced the removal of PPCPs by the electro-peroxone process.68 figures,32 tables,and 247 references...