Internal concentration polarization (ICP) is a major issue in forward osmosis (FO) as it can significantly reduce the water flux in FO operations. It is known that a hydrophilic substrate and a smaller membrane structure parameter (S) are effective against ICP. This paper reports the development of a thin film composite (TFC) FO membrane with a hydrophilic mineral (CaCO3)-coated polyethersulfone (PES)-based substrate. The CaCO3 coating was applied continuously and uniformly on the membrane pore surfaces throughout the TFC substrate. Due to the intrinsic hydrophilicity of the CaCO3 coating, the substrate hydrophilicity was significantly increased and the membrane S parameter was reduced to as low as the current best of cellulose-based membranes but without the mechanical fragility of the latter. As a result, the ICP of the TFC-FO membrane could be significantly reduced to yield a remarkable increase in water flux without the loss of membrane selectivity.

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Biofilm formation from bacterial growth and colonization is a known cause for membrane performance deterioration in water treatment. A broad-spectrum biocide such as silver nanoparticles (Ag NPs) is generally added to the membrane to impart biofilm resistance. Because biofilm formation begins with the membrane surface in contact with the feedwater, a high loading of uniformly dispersed Ag nanoparticles (Ag NPs) on the membrane exterior surface is desirable for a good antimicrobial performance. This was accomplished in this work by a short alkaline treatment of a hydrolyzable membrane (polyacrylonitrile, PAN) to introduce negative charge to the surface. A subsequent exposure to a Ag precursor solution followed by reduction under mild reducing condition (CO) limited the Ag NP deposition to within a narrow region of the membrane surface. The Ag content on the resultant membrane exterior surface in this study was also the highest in the literature. Different from previously reported methods, this method of Ag NP incorporation can be applied to thin film composite (TFC) membranes without any adverse effect on the water flux. The TFC membranes modified as such have shown good antibacterial resistance for 14 days under laboratory conditions optimized for the growth of Escherichia coli.

The organic foulants and bacteria in secondary wastewater treatment can seriously impair the membrane performance in a water treatment plant. The embedded electrode approach using an externally applied potential to repel organic foulants and inhibit bacterial adhesion can effectively reduce the frequency of membrane replacement. Electrode embedment in membranes is often carried out by dispensing a conductor (e.g., carbon nanotubes, or CNTs) in the membrane substrate, which gives rise to two problems: the leaching-out of the conductor and a percolation-limited membrane conductivity that results in an added energy cost. This study presents a facile method for the embedment of a continuous electrode in thin-film composite (TFC) forward osmosis (FO) membranes. Specifically, a conducting porous carbon paper is used as the understructure for the formation of a membrane substrate by the classical phase inversion process. The carbon paper and the membrane substrate polymer form an interpenetrating structure with good stability and low electrical resistance (only about 1Ω/□). The membrane-electrode assembly was deployed as the cathode of an electrochemical cell, and showed good resistance to organic and microbial fouling with the imposition of a 2.0 V DC voltage. The carbon paper-based FO TFC membranes also possess good mechanical stability for practical use.