Comparison of membrane fouling during ultrafiltration with adsorption studied by quartz crystal microbalance with dissipation monitoring (QCM-D)

Abstract

Even though membrane technology is used in numerous industrial applications, membrane fouling is still a major challenge. Valuable information on the formation kinetics and structure of the fouling layer can be obtained by in situ real-time monitoring. Quartz crystal microbalance with dissipation monitoring (QCM-D) enables the study of adsorptive fouling in situ on a model membrane. However, so far, there has been no in-depth investigation as to what extent observations from QCM-D relate to fouling during membrane filtration. This gap is here approached by comparing membrane fouling during ultrafiltration with QCM-D measurements using the same feed (process water from thermomechanical pulping) and the same material in the polymer film as in the membrane (hydrophilized polysulfone). The performance at two temperatures (25 °C and 50 °C) was studied. Fouling was analyzed by flux measurements, changes in frequency and dissipation over time with QCM-D, and surface characterization of the membrane samples and QCM-D sensors. QCM-D revealed an increase in rigidity of the fouling layer at 50 °C with time, which was consistent with a higher irreversible resistance during ultrafiltration. This was presumably caused by structural changes of hemicelluloses and colloidal wood extractive droplets in the process water at the higher temperature. The study shows that findings from QCM-D on the attachment of foulants on polymer films are comparable to membrane fouling. Thus, QCM-D, together with complementary analytical methods, can provide valuable insights on the development of membrane fouling of e.g., industrial wastewater.