Highly permeable forward osmosis (FO) membranes for high osmotic pressure but viscous draw solutes

Recently, a wide range of large size draw solutes have been developed and employed in forward osmosis (FO) processes with the advantages of high water flux, minimum reverse flux and easy recovery. However, the high viscosity of these draw solutes tends to suffer from severer internal concentration polarization (ICP) and internal fouling within the sublayers. To solve these problems, a dual selective flat sheet membrane has been designed in this study in order to prevent the viscous draw solutes from entering the porous support layer and minimize the ICP effects. It consists of three layers: a top thin polyamide layer synthesized from interfacial polymerization, a middle porous cellulose ester layer, and another bottom thin polyamide layer. The dual selective thin film composite (TFC) membrane has a reasonably high water flux of 34.5. LMH and a low salt reverse flux of 3.5. gMH using DI water and 1. M NaCl as the feed and draw solutions respectively under the FO mode. Comparing to single selective TFC membranes, the dual selective membrane significantly mitigated ICP effects and reduced fouling propensity using viscous draw solutes such as sucrose, ferric citric acid complex (Fe-CA) and polyethylene glycol monolaurate (PEG 640ML) as draw solutes. The newly developed dual selective membrane has great potential to maximize the effectiveness of viscous draw solutes in various FO processes.