Study of humic acid adsorption on nanofiltration membranes by contact angle measurements

Abstract

Membrane fouling is a major problem, which extent depends on the respective natures of the solute and membrane material. Membrane surface characterization under different fouling conditions may help in understanding the fouling mechanism. Such characterization was performed for the case of humic substances filtered on two nanofiltration membranes, using special contact angles measurements. The measured contact angles allowed the calculation of polar and non-polar contributions to the surface energy of dry, hydrated and fouled membranes. The results reveal significant differences in the two membrane behaviours and information about the way that fouling material may be adsorbed on menibrane surface. Le Keywords: humic acid, adsorption, contact angle, nanofiltration, membrane fouling.or the drinking water industry, improvement of the F removal of colloidal organic matter (COM) prior to the disinfection step is currently an important issue. Among the different removal methods, nanofiltration (NF) is becoming a more and more attractive alternative, because it is a compact, safe and easy-to-control process which allows the production of a high quality water. Despite all its advantages, the application of NF is partially restricted by the problem of membrane fouling which makes the permeate flow decrease with time and which increases the membrane cleaning frequency, especially in the case of surface water (Taylor et al., 1992). Humic substances (HS) are among the suspected fouling agents. These substances are important constituents of the COM, whose molar masses may range from a few hundreds to tens of thousands of daltons and which can be separated by NF (Clark et al., 1991). Lahoussine-Turcaud et al. (1990) have shown how ultrafiltration membranes can be very quickly fouled by HS and one can expect that these substances also play an important role in membrane fouling during the NF of surface waters.Cheryan ( 1986) and other membrane researchers recognized that the nature and importance of fouling are strongly affected by the membrane surface properties. For many researchers, contact angle measurements appeared to be a simple method to characterize membrane surfaces. Oldani and Schock (1989) characterized dry membranes by the conventional sessile drop method. Jucker and Clark (1994) used the same technique to characterize membrane surfaces at different levels of HS static adsorption. They observed *Author to whom correspondence should be addressed. E-mail address: cbouchar@gci.ulaval.ca that upon adsorption of HS, the membranes become more hydrophilic. Zhang and Hallstrom (1990) used the air captive bubble technique to measure the advancing and the retreating contact angles which, respectively, correspond to a decreasing and to an increasing air bubble base surface. They observed hysteresis effects which may be due to the membrane rugosity. More recently, Zanders et al. (1995) used the same technique to study the effect of the water pH and ionic strength on membrane surface properties. Keurentjes et al. (1989) used ...

Surface Interactions and Fouling Properties of Micrococcus luteus with Microfiltration Membranes

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Forward osmosis desalination of oil and gas wastewater: Impacts of membrane selection and operating conditions on process performance

“…Averaged contact angle measurements were used to determine the surface energetics of each membrane using the Lifshitz-van der Waals acid-base approach following similar procedures outlined in the literature [31,32]. Estimates of the long-range surface forces (non-polar) and short-range acid-base (polar) forces for each membrane were determined through the extended Young equation [31][32][33][34] …”

Influence of biofouling on pharmaceuticals rejection in NF membrane filtration

“…The partition of a solute between the feed solution and the membrane can be easily calculated via contact angle measurements (van Oss, 2007). Sessile drop contact angle measurements on dry surfaces, which are commonly employed to determine solid surface properties (van Oss, 2006), however suffer a major drawback in membrane science: the surface needs to be dried and contact angle determination is thus not performed on a surface in its operating condition (Bouchard et al, 1997). Drying of the membrane is likely to alter the morphological structure and thus the properties of the fouling layer present on the surface of the membrane (Rosa and de Pinho, 1997), especially for bacterial cells and the highly hydrated film in which they are embedded (Flemming et al, 2007;Rosa and de Pinho, 1997).…”