Stability and fouling mechanism of magnetophoretic-actuated PES composite membrane in pH-dependent aqueous medium

• The magnetophoretic-actuated PES composite membrane has better antifouling properties.
• The stability of the magnetic-responsive layer in feed streams with various pH is studied.
• The membrane fouling mechanism using classical and combined fouling models is studied.
• Magnetophoretic actuation significantly reduced the membrane's cake fouling.

A modified polyethersulfone (PES) membrane end-capped with magnetic-responsive iron oxides on a membrane's outermost top layer was employed to remove organic foulant from the membrane surface. The present work focused on the influence of pH-fluctuated aqueous mediums on the stability of the magnetite-augmented composite membrane and evaluated the relative fouling mechanism of the membrane through classical and combined membrane fouling models. Quartz crystal microbalance with dissipation (QCM-D) confirmed the stability of the membrane's magnetic-responsive functional layer throughout a feed stream pH range of 2–10. The magnetic membrane showed a loss of functionality as the magnetophoretic actuator when it was operated under an aggressive alkaline aqueous environment (pH 12). The filtration results indicate a transition of the membrane fouling mechanism, from standard pore blocking to the formation of a cake layer throughout the filtration processes. The curve that fit the results between the experimental data and the combined membrane fouling model identified cake fouling as the most critical factor that contributes to membrane fouling. Further membrane filtration tests confirmed the effectiveness of the in house-developed magnetite-augmented composite membrane to function as the magnetophoretic actuator that “prevents the organic foulants (humic acid in the present work) from approaching” and/or “detached the adsorbed foulants from” the membrane surface and greatly reduced the tendency of the cake formation for the most water-processing pH (2–10) at all times.