Fabrication of hollow fiber membrane microstructures and the investigation of antifouling mechanism for vegetable oil wastewater

In this study, four kinds of hollow fiber ultrafiltration membranes with different hydrophilic chains and surface microstructures were prepared via the "physical blending-surface grafting" method. The influence of surface microstructures for the formation process of the vegetable oil fouling layer on the surface of membranes and antifouling performance were investigated. By characterizing the changes in adhesion force on the surface of membranes and the surface charge of emulsified oil droplets before and after separation, the differences in the flocculation and coalescence processes for emulsified oil droplets on different membrane surfaces were revealed. The synergistic effect of "the flocculation of physical contact by polymer chains, the hydrophilic repulsion of hydration layer and electrostatic neutralization", led to the formation of large-sized oil droplets on the surface of membranes with weakly charged surface and loose accumulation ultimately, which will in turn weaken the adsorption of pollutants and the irreversible fouling can be delayed. The synergistic antifouling mechanism of "hydrophilic repulsion of the hydration layer-grafting long chains barrier & coalescence" was proposed based on the membrane's antifouling performance, the adhesion and spreading process of pollutants on the membrane surface, as well as the differences of the surface hydration layer microstructure. The membrane modified by grafting PEI and PVA exhibits excellent retention performance (oil rejection rate similar to 100 %) and resistance to oil-in-water emulsion fouling (flux recovery rate (FRR) = 99.12 %), weakest adhesion force (9.32 nN) and minimal adhesion mass (1.7 mg) of pollutants on the surface of membrane. This work offers new research insights into the theoretical study and fabrication of hollow fiber ultrafiltration membranes with high oil fouling resistance.