In Situ Surface Chemical Modification of Thin-Film Composite Forward Osmosis Membranes for Enhanced Organic Fouling Resistance

Abstract

Forward osmosis (FO) is an emerging membrane-based water separation process with potential applications in a host of environmental and industrial processes. Nevertheless, membrane fouling remains a technical obstacle affecting this technology, increasing operating costs and decreasing membrane life. This work presents the first fabrication of an antifouling thin-film composite (TFC) FO membrane by an in situ technique without postfabrication treatment. The membrane was fabricated and modified in situ, grafting Jeffamine, an amine-terminated poly(ethylene glycol) derivative, to dangling acyl chloride surface groups on the nascent polyamide active layer. Surface characterization by contact angle, Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), zeta potential, atomic force microscopy (AFM), and fluorescence microscopy, confirms the presence of Jeffamine on the membrane surface. We demonstrate the improved fouling resistance of the in situ modified membranes through accelerated dynamic fouling FO experiments using a synthetic wastewater feed solution at high concentration (250 mg/L) of alginate, a model macromolecule for the hydrophilic fraction of wastewater effluent organic matter. Our results show a significantly lower flux decline for the in situ modified membranes compared to pristine polyamide (14.3 ± 2.7% vs 2.8 ± 1.4%, respectively). AFM adhesion force measurements between the membrane and a carboxylate-modified latex particle, a surrogate for the organic (alginate) foulant, show weaker foulant-membrane interactions, further confirming the enhanced fouling resistance of the in situ modified membranes.

Natural organic matter interactions with polyamide and polysulfone membranes: Formation of conditioning film

“…4a, S5), indicating an impact of ions on the adhesion mechanism. These adhesion forces were described by log-normal distributions, as similarly described between CML colloidal AFM probe and PA membrane in a previous investigation [41]. Adhesion distances and adhesion energies increased with increasing Na + concentration (Fig.…”

Shielding membrane surface carboxyl groups by covalent-binding graphene oxide to improve anti-fouling property and the simultaneous promotion of flux

“…The Ca 2þ /organic foulants compound synthetic wastewater was constituted by CaCl 2 , NaCl, NaHCO 3 and sodium alginate (Mo et al, 2012;Lu et al, 2013). Before fouling, the compacted membranes were equilibrated with a background electrolyte containing 1 mM CaCl 2 , 16 mM NaCl and 1 mM NaHCO 3 (Mo et al, 2012) until the flux stabilized.…”

“…Fouling tests were conducted on the pDA/TMC, pDA/TMC/GO10 and pDA/TMC/C10 membranes with synthetic wastewater containing Ca 2þ /organic compound foulants, as organic foulants and calcium ions often coexist in wastewater secondary effluent or some natural water (Lu et al, 2013). Calcium and other multivalent cations have been reported to accelerate the fouling process by 'bridge' between the carboxyl groups of the polyamide membrane surface and alginate (Mo et al 2011(Mo et al , 2012.…”

“…For membranes surface with much carboxyls, the fouling process can be greatly enhanced by low concentrations of Ca 2þ or other multivalent cations, because these cations can effectively coordinate with the carboxyls on the membrane surface and organic foulants (Mo et al 2011(Mo et al , 2012. As Ca 2þ or other multivalent cations widely coexist with organic foulants in actual wastewater (Lu et al, 2013), reducing the carboxyls density on membrane surface can be a feasible choice to control this type of membrane fouling.…”

“…However, in some cases, membrane flux, rejection efficiency, robustness and anti-fouling properties are mutually exclusive. Therefore, membrane modification methods may influence the water permeability (Lu et al, 2013;Van Wagner et al, 2011;Liu et al, 2015), surface roughness (Van Wagner et al, 2011), or rejection efficiency Ye et al, 2015). Materials possessing better characteristics may help to handle these problems better.…”