Characteristics Of Algal Organic Matter Under Metal Nanoparticles Stress And Its Effects On Ultrafiltration Membrane Fouling

Ultrafiltration,as the third-generation core technology for drinking water treatment.The algal extracellular organic matter(dEOM)get more attention since it cannot be effectively removed by traditional drinking water treatment,such as coagulation,percipitation and filtration.At present,the rapid development and widespread application of nanotechnology cause more and more metal nanoparticles enter the surface water,and stress the algae and influence the dEOM characteristics.In this paper,nano-silver,nano-titanium dioxide,and nano-zero-valent iron were selected,while a cyanobacteria(Microcystis aeruginosa)and a green algae(chlorella)were studied.The changes of dEOM were characterized to study how dEOM affect the ultrafiltration membrane pollution when the algae was stressed by the metal nanoparticles.The main research results in this study are as follows:(1)A fter the stress of three different metal nanoparticles,the characteristics of algae dEOM changed:AgNPs promoted the release of DOC,while both TiO2-NPs and NZVI inhibited the release of DOC.Zeta potential is negatively charged,the overall absolute value of dEOM of Microcystis aeruginosa increases,but the opposite of chlorella.The proportion of dEOM maccromolecules of the two algae decreased under the stress of AgNPs and NZVI,and increased under the TiO2-NPs stress.And the macromolecular substance of Chlorella dEOM has a lower molecular weight than Microcystis aeruginosa.Among the two kinds of algae dEOM fluorescent substances,humic substances increased overall.Chlorella dEOM has a higher proportion of tryptophan substances than Microcystis aeruginosa.Subsequently,based on PCA analysis,it wasfound that macromolecular substances were positively correlated with Building-Blocks,humus and tryptophan-like substances,and SUVA values;small molecule substances were positively correlated with protein-like and humus-like substances.PC1 represents the change in molecular weight of organic matter,and PC2 represents the change in aromatic compounds.AgNPs has a great influence on the molecular weight of Microcystis dEOM,and it has a great influence on the aromatic compounds in Chlorella dEOM.(2)After the stress treatment of three kinds of metal nanoparticles,the ultrafiltration membrane pollution behavior caused by algae dEOM has changed significantly,and combined with RDA and pollution model to analyze the membrane fouling mechanism:Regardless of the stress conditions of the metal nanoparticles,the membrane flux reduction caused by Microcystis aeruginosa dEOM is higher than that of Chlorella.And the dEOM of Microcystis aeruginosa can cause both reversible and irreversible pollution,of which reversibility accounts for the main proportion,while chlorella dEOM almost has only irreversible pollution.The main contributing factors are the filter cake layer formed by macromolecules and the pore blockage caused by small and medium molecular substances,respectively.