Research On Preparation And Antifouling Mechanism Of Modified Forward Osmosis Membrane Based On Tannic Acid-Fe(Ⅲ)

The strategic concept of municipal wastewater resource utilization and carbon neutrality has been widely disseminated in recent years,which has contributed to the transformation and upgrading of the traditional wastewater treatment industry.The conventional method of operating with energy consumption for water quality requires urgent optimization.Efforts should be made to decrease the energy consumption of treatment and explore the energy from wastewater to achieve the recycling and utilization of resource.Forward osmosis membrane separation technology has significant potential for application in the reclamation of wastewater due to its advantages of no external pressure and low energy consumption.However,during the current long-term separation process,membrane fouling affects the separation efficiency of FO membrane,which is a key challenge limiting the widespread application and further and better development of forward osmosis technology.Therefore,this study is directed to enhance the anti-fouling performance of forward osmosis membrane by modifying forward osmosis membrane with surface functionalization,in order to explore a green,environmentally friendly,easy-to-operate,swift and efficient membrane pollution control strategy.In addition,the anti-fouling mechanism is explored to provide a theoretical reference for the large-scale application of forward osmosis technology in the field of the reclamation of municipal wastewater.（1）The complexation reaction between tannic acid（TA）and Fe Cl₃ was used to prepare a fast and efficient precursor layer on the surface of CTA forward osmosis membrane to lay the foundation for the subsequent modification.The effects of buffer solution p H,TA/Fe³⁺concentration ratio and TA/Fe³⁺self-assembled layers on the TA/Fe³⁺complex modification were investigated,and the modified membranes were analyzed by SEM,water contact angle and AFM characterization.The optimum modification conditions of TA/Fe³⁺complex modification were determined as p H=8 of buffer solution,4:1 of TA/Fe³⁺concentration ratio and 5 of TA/Fe³⁺self-assembled layers.The prepared TA/Fe³⁺modified membranes will be used for subsequent modification and performance investigation.（2）The tannic acid/diethylenetriamine（TA/DETA）coating layer was introduced on the top of TA/Fe³⁺modified membrane.Additionally,the reducing ability of TA could also be used to introduce antibacterial material silver nanoparticles（Ag NPs）to the surface of the modified membrane.The characterization results of SEM,FTIR,XPS,Raman and AFM confirm that the modified layer has successfully combined on the membrane surface.The hydrophilicity of the modified membrane was further enhanced.The mass transfer coefficients and structural parameters of the membranes did not change significantly after the surface modification.TA/Fe³⁺-TA/DETA-Ag/PVP membranes showed excellent bacterial inhibition performance in the static anti-biological contamination experiments by reaching 97.30%and 98.63%for Escherichia coli and Staphylococcus aureus,respectively.The stability experiments demonstrated that the TA/Fe³⁺-TA/DETA membrane and TA/Fe³⁺-TA/DETA-Ag/PVP membrane possessed great physical and chemical stability.（3）Using municipal wastewater as the feed solution and sodium chloride solution as the draw solution,a 15-day dynamic contamination experiment was conducted to investigate the flux change,treatment efficiency and contamination resistance of the modified membranes during actual operation.The flux of TA/Fe³⁺-TA/DETA-Ag/PVP membrane only decayed by27.19%after 15 days,compared to 47.86%of the original CTA membrane.It also exhibited good contaminant retention capacity.The TA/Fe³⁺-TA/DETA-Ag/PVP membrane had the lowest microbial and organic contaminant content,the lowest total resistance of 2.464×10¹⁵m^-1 and the best flux recovery rate of 80.37%.This showed that the TA/Fe³⁺-TA/DETA-Ag/PVP membrane had good resistance to contamination.