Surface Modification And Pollution Resistance Of Hydrophobic PVDF Hollow Fiber Membranes In MBFR

Combined with high efficiency membrane aeration and the ability of biological treatment,Membrane biofilm reactor(Membrane Biofilm Reactor,MBfR)as a new type of water pollution control technology has the advantages of high oxygen utilization efficiency,good carbon and nitrogen removal,low loss of volatile gas and easy operation.The aeration membrane plays the most important role in the system.Therefore,the membrane material not only requires excellent oxygen mass transfer performance,but also has mechanical strength,bio-affinity,and anti-fouling,corrosion resistance property.But,the membrane designed for MBfR is still rare.In order to solve the problem that the hydrophobic microporous membrane has insufficient oxygen supply capacity and poor resistance to pollution in the MBfR study.On the basis of the previous research,Dopamine(DOPA)was used as the monomer to modify the hydrophobic hollow fiber microporous membrane by self-polymerization method.Using the response surface method with oxygen mass transfer performance as the main evaluation index to optimize the surface modification conditions.The results showed that the addition of oxidant S accelerated the deposition rate of poly-dopamine(PDA)on the surface of the membrane and greatly shortened the coating time.When the DOPA concentration was 0.85 g/L,n(S):n(DOPA)=1.5,the coating time was 6 h and the heat treatment temperature was 40?,the PDA-coated PVDF had the same mechanical properties as the Pristine PVDF,the oxygen transfer coefficient(KLa)increased to 2.1 times of the original membrane(improved from 0.78 × 10-2 min-1 to 1.67 × 10-2 min-1),and the mass transfer coefficient of oxygen was higher than that of the original membrane.The static contact angle and morphology of the membrane surface showed that the hydrophilicity of the modified membrane was improved(the contact angle decreased from 76.7 ° to 36.3 °)and the roughness increased from 190.33 A to 355.91 A.The results showed that the addition of oxidant SP could accelerate the self-polymerization of DOPA,increase the deposition rate of PDA on the membrane surface,and enhance the polymerization of PDA on the membrane surface.By adding oxidant SP,the stability of PDA polymerization layer increased by 96.5%,85.1%and 48.8%,respectively in polar solvents acetone,strong acid(HCl pH1.0),strong alkali(NaOH pH 13.0)three extreme environments.In addition,the dopamine-modified membrane under the optimal surface modification conditions showed that the dopamine-modified membrane was stable in polar solvents such as acetone,strong acid(HCl pH 1.0),strong alkali(NaOH pH13.0)and pure water pH7.0,but weak alkali resistance.BSA,HA,SA were used as the typical pollutants,the interaction between the modified membrane and the three pollutants,and pollutants at different pH values(pH 4.0?7.0?10.0)was evaluated by XDLVO theory.First,the difference of contribution of membrane fouling was predicted by XDLVO theory.Then the membrane fouling experiment was carried out on the original membrane and the modified membrane to verify the correlation between theory and experiment.The experimental results show that the interaction energy between the three pollutants and the original membrane is negative at pH4.0,and the adsorption capacity increases with the increase of the pH value.With the increase of pH,the repulsive force between contaminants and membrane gradually increased,thus slowing the membrane fouling,the modified membrane anti-pollution performance is better than the original membrane,The adsorption capacity of BSA on the modified membrane was the least,the adsorption capacity of SA on the membrane was the highest,followed by HA.PDA-coated PVDF has better anti-pollution performance than the Pristine PVDF.The prediction of XDLVO theory had good correlation with the pollution experiment and could be applied to the study of MBfR membrane fouling mechanism.