In situ real-time investigations on adsorptive membrane fouling by thermomechanical pulping process water with quartz crystal microbalance with dissipation monitoring (QCM-D)

Abstract

Membrane processes are essential for the success of lignocellulosic biorefineries, but membrane fouling is still a major problem and the single most important reason for the relatively slow acceptance of membrane technology in this industrial application. It is therefore of the utmost importance to find methods that enable the study of the fouling development when processing new types of feed solutions. Although ex situ analysis allows the composition of the fouling layer to be determined, the processes leading to its build-up remain unknown. In this study, quartz crystal microbalance with dissipation monitoring (QCM-D) was used to study adsorptive fouling in situ. By using QCM-D, the development of fouling over time can be studied. Fouling of three fractions of a thermomechanical pulping process water (feed, microfiltration retentate and permeate) were studied on QCM-D sensors coated with a polymer used in commercial polysulfone membranes. The retentate contained mainly colloidal extractives and the permeate hemicelluloses. In the case of the retentate, adsorption was almost immediate and the greatest increase in mass was observed. In case of the permeate, the increase in mass was slowest but at steady state the adsorbed mass was similar to the adsorbed mass of the process water. After rinsing with water, an irreversibly attached network of hemicelluloses remained on the polymer surface while the colloidal extractives were washed away. Overall, the study shows that in situ real-time monitoring of adsorptive membrane fouling combined with additional ex situ analysis generates valuable understanding on the evolution of membrane fouling in lignocellulosic biorefineries.