The influence of dairy salts on nanofiltration membrane charge

Rejection of dairy salts by a nanofiltration membrane

“…1 shows that this membrane resistance changed by less than 0.2 × 10 13 m −1 over the entire pH range examined. A resistance minimum was observed at approximately pH 4.5 which corresponded quite closely to the measured surface isoelectric point (IEP) of the membrane [17]. Childress and Elimelech [20] observed a similar peak in flux for a different polyamide NF membrane, and attributed this to pore expansion due to uncharged functional groups within the pores at the pore IEP.…”

“…These are polyamide thin-film composite membranes with an observed molecular weight cutoff of 150-200 Da and chloride rejection of 40-55%. Further characteristics of this membrane material are outlined in a companion paper [17]. In all experiments filtration was performed at a flowrate of between 2 and 3 L/min which equated to a cross-flow velocity across the membrane surface of between 0.4 and 0.6 m/s.…”

“…Changes to the membrane charge can occur due to adsorption of solutes [17], membrane fouling [18] and also through charge shielding. These can influence the rejection of other charged species.…”

Principles of Membrane Filtration

“…Generally, membranes should be neutral or of the same charge as the particles being processed to prevent attraction, which can result in fouling. For process design, the pH of the feed stream needs to be considered as the membrane charge is influenced by the pH of the fluid in touch with the membrane surface (Rice et al ., 2011). Some membrane materials, for example polyamide, can exhibit amphoteric behaviour; here the pH of the cleaning agent should condition the surface with a charge appropriate for the feed being processed in the following production period (Tang et al ., 2006).…”

“…Differences in shape can also be due to high shear prevalent at the membrane surface (Cheryan, 1998). The pH of an aqueous solution not only has a bearing on particle size and electrostatic potential of many components in the solution itself, but can also change the surface charge on the membrane as discussed above (Bouzid et al ., 2008;Rice et al ., 2011).…”