Abstract
Membrane fouling is the major factor limiting the wider applicability of the membrane-based technologies in water treatment and in separation and purification processes of biorefineries, pulp and paper industry, food industry and other sectors. Endeavors to prevent and minimize fouling requires a deep understanding on the fouling mechanisms and their relative effects. In this study, Brunauer-Emmett-Teller (BET) nitrogen adsorption/desorption technique was applied to get an insight into pore-level membrane fouling phenomena occurring in ultrafiltration of wood-based streams. The fouling of commercial polysulfone and polyethersulfone membranes by black liquor, thermomechanical pulping process water and pressurized hot-water extract was investigated with BET analysis, infrared spectroscopy, contact angle analysis and pure water permeability measurements. Particular emphasis was paid to the applicability of BET for membrane fouling characterization. The formation of a fouling layer was detected as an increase in cumulative pore volumes and pore areas in the meso-pores region. Pore blocking was seen as disappearance of meso-pores and micro-pores. The results indicate that the presented approach of using BET analysis combined with IR spectroscopy can provide complementary information revealing both the structure of fouling layer and the chemical nature of foulants.
Highlights
Wood origninated process and wastewaters contain valuable and underutilized compounds such as hemicelluloses, lignin, phenols and various monomeric compounds
Novel techniques are needed for exploration of the fouling mechanisms and for gaining further knowledge on the chemical compositions and structures of the fouling layer formed in different processes
The porosity of the fouling layer has been shown to increase with increasing foulant size, and the pore size distribution of voids in the fouling layer is narrower if the foulants are monodispersed and form similar intermolecular openings[10]
Summary
Wood origninated process and wastewaters contain valuable and underutilized compounds such as hemicelluloses, lignin, phenols and various monomeric compounds Recovery of these compounds requires efficient separation technologies, and ultrafiltration (UF) has proven to be a very promising technique for fractionation and purification of these compounds from lignocellulosic streams[1]. Membrane–foulant interactions have a significant effect on the adsorption of foulants on the surface and on the pore walls of the membrane[5]. The conventional measurements cannot distinguish whether changes in membrane performance are caused by adsorption, pore blocking or formation of a cake or gel layer, that all cumulatively affect the flux or pressure[6]. Porosity and surface area are the key parameters in membrane studies as they indicate the structural properties of the membrane and may even reveal the sites for possible foulant accumulation. Despite the ability of BET to reveal the changes in porosities, to our knowledge there are only limited examples where BET analysis has been applied to characterize changes caused by membrane fouling
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