(506d) Membrane Fouling Behavior Evaluated by Constant Flux and Constant Transmembrane Pressure Filtration

Membrane systems can be operated in two ways: constant permeate flux with variable transmembrane pressure (TMP) or constant transmembrane pressure with variable permeate flux.  Membrane fouling may be measured using either of these two methodologies.  This presentation shows a comparison of constant-flux and constant-TMP operation of commercial flat-sheet membranes during oily water filtration.  The critical flux—the flux below which minimal fouling occurs—was determined by a flux-stepping method using constant flux crossflow filtration.  The membrane performance during fouling was evaluated using both operating modes at fluxes higher than and lower than the critical flux.  Membrane resistance evolution during fouling is compared for constant-flux and constant-TMP operation.  At fluxes lower than the critical flux, where fouling was relatively minor, the membrane resistances during constant-flux and constant-TMP fouling developed comparably.  At fluxes higher than the critical flux, the membrane resistance evolution differed for the two operating modes.  Reasons for similarities and differences in membrane behavior in each operational mode will be discussed.  Surface modification is a popular means of attempting to alleviate membrane fouling.  Polydopamine is currently of wide interest as a substrate-independent surface modification agent.  Polydopamine-coated surfaces universally show high hydrophilicity and, in early studies, polydopamine-modified membranes have shown improved resistance to fouling when challenged with synthetic oily water.  Surface-modified microfiltration and ultrafiltration membranes were tested in constant-flux and constant-TMP fouling experiments.  Fouling of modified membranes will be compared to unmodified membranes and the ramifications of testing protocol on membrane fouling behavior will be discussed.