Using electrokinetic leakage to probe internal fouling of ultrafiltration membranes Submission topic: Membrane fouling and cleaning

It has been reported that complications in the interpretation of both streaming potential and streaming current may arise when tangential electrokinetic measurements are conducted with porous membranes [1, 2]. Indeed, an electrokinetic leakage, i.e. a non-zero streaming current through the membrane porosity, can develop and makes it more difficult to determine the correct zeta potential of the membrane skin layer. In this work, it was shown for the first time that this parasitic phenomenon can be used as a probe allowing characterization of fouling inside porous membranes. Both polyethersulfone (PES) and polyacrylonitrile (PAN) UF membranes were characterized by tangential streaming current measurements. The electrokinetic leakage was quantitatively determined from series of tangential streaming current measurements performed by varying the distance (from ca 40 to 100 m) between two identical membrane samples. Our results first revealed that a significant electrokinetic leakage occurred through both the pristine membranes. This parasitic phenomenon was greater with the PAN membrane than with the PES membrane, which was explained by the less hydrophobic character and the more porous structure of the PAN membrane. We showed that neglecting the electrokinetic leakage phenomenon in data interpretation would lead to misleading conclusions regarding the surface charge properties of the membrane skin layer. Both membranes were further fouled with lipids by using different experimental conditions (diffusion of lipids for various soaking times or ultrafiltration of oil-in-water emulsions under various transmembrane pressure differences). The presence of lipids inside the membranes was found to decrease the magnitude of the electrokinetic leakage, which was attributed to the hydrophobicity of lipids resulting in the disconnection of the ionic conduction pathways through the membrane porosity. Eventually, it was demonstrated that monitoring the electrokinetic leakage through a membrane can provide useful information about both internal and surface fouling. This work therefore paves the way for advanced characterizations of membrane fouling and cleaning.