Plasma-induced Zwitterionic Grafting Of PVDF Membranes And Study On Its Anti-fouling Properties

Membrane bioreactor?MBR?is a new type of wastewater treatment technology developed in recent years.It combines traditional biological methods with membrane technology and has significant processing advantages.However,a series of membrane fouling problems in MBR restrict the widespread application of MBR.Polyvinylidene fluoride?PVDF?membrane is the most widely used membrane material in MBR.However,due to its poor hydrophilicity and low surface energy,PVDF membranes are prone to the formation of adsorptive contamination and filter cake contamination in the MBR,which severely shortens the service life of the membrane and increases the operating costs.For this purpose,plasma technology was used to graft dimethylaminoethyl methacrylate?DMAEMA?onto the surface of PVDF membrane,and then it was quaternized with 3-bromopropionic acid?3-BPA?and finally obtained zwitterionic modified membrane?PVDF-g-PCBMA?,and study on its antifouling performance and practical application systematically.The research of plasma modification technology show that when the plasma grafting power is 15W and the grafting time is 90s,it is the best condition for plasma reaction,and the grafting rate is the highest.The surface properties of the modified membranes were characterized.The FTIR-ATR spectra demonstrated that the tertiary amine groups?-N?CH₃?₃?and carboxylic acid groups?-COOH?were grafted onto the PVDF-g-PCBMA membranes,they are the main constituent group of the zwitterion;SEM image shows that a smoother graft layer is formed on the pore framework surface of the PVDF-g-PCBMA film;the water contact angle analysis shows that compared to the original PVDF film,PVDF-g-The contact angle of PCBMA film decreased from 88.3°to 39.0°,and the hydrophilicity was greatly improved.The antifouling performance of the modified membrane towards the standard membrane contaminants bovine serum albumin?BSA?and sodium alginate?SA?was investigated by static adsorption and dynamic filtration experiments.The results of static adsorption experiments showed that the adsorption rates of BSA and SA in PVDF-g-PCBMA membranes were 25.2%and 14.4%,respectively,which were59.8%and 49.3%lower than those of the original membranes,respectively,indicating that the PVDF-g-PCBMA membrane surface was resistant to BSA and SA.Adsorption capacity was significantly improved;the results of dynamic filtration experiments showed that when filtration of BSA solution,the flux attenuation rate of PVDF-g-PCBMA membrane was lower than that of the original membrane by24.6%,which was higher than that of original membrane flux recovery and rejection rate,respectively 46%and 2.8%,indicating that the PVDF-g-PCBMA film has better antifouling properties.In order to study the antifouling performance of the modified membrane in MBR,its antifouling characteristics of the key membrane contaminants soluble microbial products?SMP?and extracellular polymeric substance?EPS?in the MBR were mainly investigated.The research showed that the surface zwitterionic modification process increased the flux recovery after membrane cleaning.The rate reduced the adsorption efficiency of protein and polysaccharide in SMP and EPS,reduced the adsorption and deposition of proteins and polysaccharides on the surface of SMP and EPS,and calculated and analyzed according to XDLVO theory showed that the modified membrane adsorbed on SMP and EPS.The energy barrier is much higher than that of the original membrane,and the relationship between the surface of the modified membrane and SMP and EPS can always exist in the form of repulsive energy,proving that in the MBR,the modified membrane has better antifouling ability.In summary,after the original PVDF membrane was zwitterionic surface modified,the flux attenuation of the PVDF-g-PCBMA membrane during the filtration of pollutants became slow,and the recovery rate of the clean water flux after physical and chemical cleaning was significantly increased.The ability of resisting SMP and EPS contamination was significantly improved,demonstrating that PVDF-g-PCBMA membrane has superior antifouling capability.