Effects of Natural Organic Matter and Ionic Species on Membrane Surface Charge

Abstract

The surface charges of clean and natural organic matter (NOM)-adsorbed membrane surfaces of two different types of membranes (a UF and a NF membrane composed of the same material but having different pore sizes) were investigated. Concentrated NOM and its fractionated constituents were used as adsorbate and interacting macromolecules nearthe membrane surface. The zeta potential and the acidity of membranes were measured using electrophoresis and potentiometric titration methods, respectively, from the perspective of charge characterization, along with demonstration of ionic strength effects. The membrane surface was also characterized with attenuated total refractive Fourier transform infrared spectra to determine intrinsic functional groups and those changes before and after NOM adsorption. As a comparative study for the electrokinetic property of membrane, the zeta potentials for both examined polymeric membranes were determined by the electrophoresis and the streaming potential measurement methods as functions of ionic strength and the pH of measuring solution. Selectivity tests were performed to decide the relative importance of charge valence of cation in terms of the surface charge of membrane. It was demonstrated that divalent cations (Ca2+, Mg2+) increase zeta potentials relatively compared to monovalent cations (Na+, K+) because divalent cations have a greater potential in approaching membrane surfaces (i.e., inside the Stern layer). Thus, divalent cations can provide a greater double layer compaction and, when near the shear plane (available for both the zeta potential measurement methods), exist to a lesser extent than monovalent cations.

Identification of key factors affecting the organic fouling on low-pressure ultrafiltration membranes

“…Previous studies have demonstrated that organic fouling behavior in filtration was dependent on chemical characteristics of feed water, membrane properties, foulant-foulant and foulant-membrane interactions [8,17,32,35]. As discussed in Section 3.1, in HA/ BSA mixtures ultrafiltration experiments, fouling resistance increased slowly compared to other organic mixtures, while HA/ SA mixtures exhibited the highest fouling resistance, regardless of the concentration ratios (Fig.…”

“…6b illustrates the effect of the organic foulants on membrane surface ZP. All organic foulants caused notable changes in membrane surface ZP, manifesting significant adsorption on membrane surface [34,35]. Adsorption of the highly negatively charged foulants led to an increase in the magnitude of the negative membrane surface ZP, while less negatively charged solutions just caused a slight increase.…”

Selective separation of cationic peptides from a tryptic hydrolysate of β‐lactoglobulin by electrofiltration

“…The MWCO of this membrane is approximately 2,500 g/mol and its top active layer is made of polyamide (Shim et al, 2002). This membrane is reported to be a ''loose'' NF membrane as compared to the most common NF membranes, which generally exhibit a MWCO lower than 1,000 g/mol (Afonso et al, 2001;Tsuru et al, 1994).…”

Effects of a dynamic membrane formed with polyethylene glycol on the ultrafiltration of natural organic matter

“…The zeta potentials for the PT and PBCC membranes were measured using electrophoresis method with ELS-8000 (Otsuka electronics, Japan) and Smoluchowski equation [9]. Using the sessile drop method with pure water, a goniometer (NRL, Rame Hart, Mountain Lakes, NJ) with image software (DROP) was used to measure the contact angle of both membranes.…”