Insights into Fouling Control of the Salt-Responsive Membrane across the Entire Filtration–Backwashing Cycle

Ultrafiltration, a key membrane technology for surface water treatment, is highly susceptible to fouling caused by natural organic matter. Herein, a zwitterionic polymeric membrane (ZPM) was fabricated via a two-step protocol. During surface water filtration, ZPM demonstrated high pure water permeance (about 1433 L·m^–2·h^–1·bar^–1) and superior fouling-resistant ability compared with the commercial ultrafiltration membrane. The enhanced fouling control was attributed to the greater hydrophilicity and narrower pore size of ZPM. Molecular dynamics simulations and XDLVO analysis revealed that the reduced values of van der Waals energy during the interaction between foulants and ZPM were the main mechanism. Furthermore, the zwitterionic polymer underwent deformation under a NaCl solution (10 g·L^–1) due to the antielectrolyte effect, causing ZPM to mechanical swelling. This mechanical effect alone can remove 70% of the membrane fouling resistance, comparable to the performance of pure water backwashing. The swelling of ZPM also reduced the membrane pore size, leading to a 56% increase in flux velocity, further removing membrane fouling resistance. This study provides new insights into enhanced membrane fouling control across the entire filtration cycle by implementing a dual strategy that combines high-efficiency membrane material with a cost-effective operational process.