Anti-scaling ultrafiltration/microfiltration (UF/MF) polyvinylidene fluoride (PVDF) membranes with positive surface charges for Ca2+/silica-rich wastewater treatment

• Positively charged amphiphilic modifiers are synthesized and anchored to membrane.
• Membranes show high surface positive charge by anchoring positive modifiers.
• Membranes well maintain their structure despite introduction of positive charges.
• Surface positive charge on the membrane led to enhancement in water permeability.
• Positively charged membranes effectively reduce membrane scaling.

We develop an anti-scaling ultrafiltration/microfiltration (UF/MF) membrane by introducing a high-density positive charge to a poly(vinylidene fluoride) (PVDF) membrane to suppress membrane scaling in Ca2+/silica-rich wastewater. Positively charged modifiers are synthesized by conjugating an amphiphilic polymer (Brij S10) and branched poly(ethylene imine) (b-PEI) at various molar ratios, and these are then implanted to PVDF membranes during the phase-inversion process. Attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectra reveal that the positive modifiers successfully anchors onto the surface of the membrane by hydrophilic-hydrophobic phase recognition. As introducing the positive charge on the membrane surface, the membranes show positive surface charge and their pure water permeability (PWP) increases due to the protonation of b-PEI. Anti-scaling properties are also confirmed to be improved by filtration tests using a metal ions/silica-rich feed solution, which results from the repulsion of metal ion by the positively charged branch on the membrane. In addition, the water flux recovery by simple membrane backwashing of the modified membrane is double that of the neat PVDF membrane.

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