Effect Of Multiple Influent Matrix On Removal Of PPCPs By Nanofiltration Membrane

In recent years,drugs and personal care products（PPCPs）have been widely found in nature,which pose a serious threat to aquatic ecological environment and human health due to their characteristics of long-term residue,bioaccumulation and strong toxicity.With the increasing demand for high quality water,nanofiltration technology has a wide application prospect in the retention of pharmaceuticals and personal care products.In this paper,influent matrix as the research object,through high performance liquid chromatography and mass spectrometry,to investigate the pH,ionic strength,coexistence of organic and inorganic ions and other conditions on the nanofiltration membrane interception of PPCPs,analysis of the multi-influent matrix conditions of nanofiltration membrane action mechanism on PPCPs and inorganic and organic matter respectively contribution to nanofiltration membrane pollution.In this paper,the influence of water quality conditions on the interception of PPCPs by nanofiltration membranes was studied,and the interception effect and mechanism of six PPCPs in water by NF90 membranes were compared under different pH and ion concentration conditions.It was found that NF90 membrane had a good removal rate of PPCPs in water,and the removal effect of neutral molecules was strongly correlated with Stokes radius（R²>0.9）.The isoelectric point of NF90 membrane is about 3.4.With the increase of pH,the membrane surface potential gradually decreases,and the interception rate of the dissociated negatively charged PPCPs molecule increases,the interception rate of the dissociated positively charged PPCPs molecule decreases,while the interception rate of the neutral molecule increases slightly but basically remains unchanged.Screening plays a major role in the process of PPCPs retention in NF90 membranes.The retention rate of NF90membrane for 6 kinds of PPCPs varies with the membrane itself and the degree of dissociation of PPCPs under different pH conditions,which is related to the characteristics of the membrane itself and the basic properties of PPCPs.The presence of Ca²⁺and Mg²⁺changes the electrostatic interaction between nanofiltration membrane and PPCPs by changing the amount of charge on the membrane surface.Ca²⁺and Mg²⁺will enter the membrane pore,reduce the potential of the membrane pore,make the membrane pore shrink and increase the screening effect.By comparing the effect and mechanism of adsorption of PPCPs by nanofiltration membrane under different pH and ion concentration conditions in static adsorption tests,it was found that NF90 membrane itself did not produce strong adsorption effect on PPCPs.However,under different pH conditions,changes in the potential of the membrane surface and PPCPs molecules will change the electrostatic interaction between the membrane and PPCPs molecules,and then change the adsorption capacity of PPCPs on the membrane surface.When electrostatic repulsion occurs between the membrane surface and PPCPs molecules,the adsorption capacity of PPCPs on the membrane surface will be reduced.When electrostatic attraction is generated between the membrane surface and PPCPs molecules,the adsorption capacity of PPCPs on the membrane surface will be increased.The presence of Ca²⁺and Mg²⁺changes the electrostatic interaction between the membrane and PPCPs by changing the amount of charge on the membrane surface.For neutral PPCPs,changes in pH and ion concentration do not change the adsorption capacity on the membrane surface.When single-component organic matter and inorganic ions coexist in water,the interception rate of PPCPs in NF90 membrane is higher than that in the presence of inorganic ions alone.However,the coexistence of sodium alginate and inorganic ions will cause great concentration polarization effect.As a result,the interception rate of nanofiltration membrane on the dissociated positively charged atenolol molecule and neutral PPCPs molecule was lower than that of inorganic ion alone.However,for the dissociated negatively charged PPCPs molecule,the interception rate did not decrease due to electrostatic repulsion.In the process of nanofiltration,organic and inorganic ions will form an organic pollution layer on the membrane surface,which will not only enhance the screening effect of the membrane surface,but also increase the amount of charge on the membrane surface,thus enhancing the electrostatic effect.When two or more components of organic matter coexist with inorganic ions,the retention rate of PPCPs in NF90 membrane is higher than that in single-component organic matter coexist with inorganic ions.This is because the filter cake layer formed by organic matter on the membrane surface further enhances the screening effect and the electronegativity of the membrane surface,so that the screening effect and electrostatic effect between PPCPs and membrane are enhanced,and the interception of PPCPs by nanofiltration membrane is improved.In addition,it can be found that the decrease of membrane flux mainly occurs at the initial stage of filtration through the changes of membrane specific flux at different time periods.The form of action of inorganic ions on the membrane surface and the contribution of inorganic substances and organic matter to membrane pollution were analyzed.It was found that Ca²⁺ion had two forms of calcium complexation and free calcium peaks between organic matter（HA and SA）and membrane,which played the role of bridging and complexation.Mg²⁺ion had only one free state peak between three organic matter and membrane,which played the role of charge shielding.And—COOH functional group is the key to complexation.The contribution of inorganic salts to membrane pollution（4.216%）was less than that of organic matter（95.784%）,among which,protein substances were the organic matter with outstanding contribution to membrane pollution,followed by polysaccharide substances,and humic acid substances had the least contribution.