Impact of feed ionic concentration on colloidal and organic fouling of osmoticallydriven membrane process

Abstract

The impact of feed ionic concentration in the presence of organic and colloidal foulant on osmotically driven membrane processes (ODMPs) was demonstrated. The normalized flux of ODMPs was significantly decresed in both DI and 10mM NaCl feed solution when the feed solution contained colloidal particles as foulants due to the deposition of colloidal particles on the membrane surface. The deposited colloidal particles strongly promoted cake-enhanced osmotic pressure near the surface of the membrane. In contrast, the normalized flux of ODMPs was slightly increased when humic acids (HA) were added as the organic foulant into the feed solution. The attachment of HA molecules changed the membrane surface conducting it more hydrophilic, and induced a stronger diffusion of water molecules into the membrane active layer. As a result, both the increased feed ionic strength and deposited colloidal fouling did not significantly alter the reversal salt selectivity of the ODMPs, while the reversal salt selectivity was significantly incresed after the addition of HA molecules to the feed solution because the HA molecules changed the properties of the membrane surface.