Novel nanocomposite membranes for osmotically driven processes : fabrication and application

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For osmotically driven membrane processes, including forward osmosis (FO) and pressure retarded osmosis (PRO), water permeate was selectively induced across a semi-permeable polymeric membrane by the osmotic pressure generated from the salinity gradient. Although both FO and PRO processes are mainly driven by the osmotic pressure difference increased by the more concentrated draw solution on the permeate site of the membrane, membrane orientations for the processes are mainly confirmed as the active layer facing the feed solution (AL-FS) for FO, and the active layer facing the draw solution (AL-DS) for PRO, respectively. Although the AL-FS orientation for FO is beneficial for controlling membrane fouling on the dense active layer, diluted internal concentration polarisation (ICP) inside a FO membrane would be a major obstacle to maintaining the osmotic driving force under FO operation. These processes have been widely used for a variety of water treatments and hybrid systems as a low-energy process. However, the processes still have some critical challenges for membrane development, which are related to the following aspects: water permeability, reverse solute diffusion, concentration polarisation, membrane fouling and membrane stability. Although many earlier studies developed various kinds of polymeric membranes at laboratory scale to produce outstanding performances for overcoming existing challenges in FO and PRO processes, most of them never produced their own scaled-up membrane modules for commercial applications. This study, therefore, initially targeted novel nanocomposite membrane development for FO and PRO processes using the dual-blade casting technique and two hydrophilic nanomaterials (graphene oxide and halloysite nanotubes). Subsequently, we selected the best strategy in our activities, and the selected one was further investigated for its commercial viability.
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