Research On Surface Modification And Performance Of Dual Functional Anti-biofouling Reverse Osmosis Membrane

Reverse osmosis?RO?membrane technology is widely used in seawater desalination and water treatment by virtue of its ability to achieve high-efficiency separation of inorganic salts and water molecules.However,membrane fouling will reduce separation efficiency and increasing energy consumption.In particular,the membrane fouling caused by the adsorption,deposition and growth of microorganisms on the surface of the RO membrane is the most serious.The development of a new RO membrane with anti-biofouling is the most effective means to combat membrane fouling.Therefore,a dual-functional anti-biofouling RO membrane was prepared based on the adsorption resistance of pollutants in the first stage and the inhibition of microbial growth in the second stage.The"passive"and the"active"antifouling mechanism were discussed,respectively.In this study,polydopamine?PDA?was coated on the surface of polyamide composite membrane?TFC?by oxidative polymerization,and nano-copper particles?Cu-NPs?were synthesized in situ by chelation to prepare a surface-modified membrane.It was found that the modified membrane surface was successfully loaded with PDA and Cu-NPs in the valence state of Cu²⁺and Cu⁰.The longer the polymerization time of dopamine,the tighter the peak-to-valley structure on the membrane surface,the lower the degree of PDA agglomeration and Cu-NPs wrapping.The oxygen-nitrogen element ratio and hydrophilicity of the membrane surface were gradually increased.The electrostatic repulsion among the modified particles was enhanced,and the roughness of membrane surface was not significantly changed.The adsorption resistance and antibacterial property were evaluated by static experiments on the adsorption of organic matter and the cultivation of bacteria on the membrane surface.On the basis of no significant change in transfer performance,the BSA adsorption for the 2 h of dopamine polymerization was reduced by 36.6%,and the rejection rate of bacteria reached more than 97.0%.The XDLVO theory was used to explore the"passive"mechanism of the adsorption resistance on the membrane surface in the first stage of biofilm formation.The van der Waals attraction was weakened as the polar repulsion was enhanced,and the formed hydration layer blocked the further adsorption of the pollutant.Then,the"active"mechanism of inhibiting microbial growth in the second stage was investigated by cell activity,metabolic activity and cell morphology.The contact and non-contact between the modified membranes and the bacteria caused the cell membrane to rupture,inhibiting ATP synthesis to reduce metabolic activity,while Cu²⁺from Cu-NPs led to efflux and dehydration of cell bodies to reduce cell viability.The membrane fouling during long-term dynamic operation and the stability were studied to provide for the application.Confocal laser scanning microscopy?CLSM?imaging indicated that live bacteria and extracellular polymeric substance?EPS?on the modified membrane were significantly reduced compared with the original membrane,and the total biomass was reduced by 53.4%.Flux decline was reduced by 40.0%,which meant the degree of irreversible fouling decreased,exhibiting a good biofouling performance.The Cu-NPs dissolved faster in the initial operation,and then gradually slowed down.There was no leakage of Cu-NPs,and the regenerated membrane still had high fouling resistance.