Abstract
The use of forward osmosis (FO) for water purification purposes has gained extensive attention in recent years. In this review, we first discuss the advantages, challenges and various applications of FO, as well as the challenges in selecting the proper draw solution for FO, after which we focus on transport limitations in FO processes. Despite recent advances in membrane development for FO, there is still room for improvement of its selective layer and support. For many applications spiral wound membrane will not suffice. Furthermore, a defect-free selective layer is a prerequisite for FO membranes to ensure low solute passage, while a support with low internal concentration polarization is necessary for a high water flux. Due to challenges affiliated to interfacial polymerization (IP) on non-planar geometries, we discuss alternative approaches to IP to form the selective layer. We also explain that, when provided with a defect-free selective layer with good rejection, the membrane support has a dominant influence on the performance of an FO membrane, which can be estimated by the structural parameter (S). We emphasize the necessity of finding a new method to determine S, but also that predominantly the thickness of the support is the major parameter that needs to be optimized.
Highlights
The growing world population and their increasing environmental burden are creating a need for more drinking water as well as a demand for cleaner energy sources and a reduction of fossil fuel use [1,2]
graphene oxide (GO) nanosheets have been successfully grafted onto the polyamide selective layer of a thin-film composite (TFC) membrane [175]; the resulting forward osmosis (FO) membrane showed a high salt rejection, a smooth surface, sufficient hydrophilicity, and a low biofouling tendency
Another simultaneous method for forming a dense selective layer was developed by Gherasim et al [179], who managed to form a polyelectrolyte-complex layer in the lumen part of hollow fibers by using a polyanion in the dope and a polycation in the bore liquid
Summary
The growing world population and their increasing environmental burden are creating a need for more drinking water as well as a demand for cleaner energy sources and a reduction of fossil fuel use [1,2]. Processes 2020, 8, 404 uses the osmotic pressure of a high solute concentration as an energy source. The movement of water through a semi-permeable membrane to an osmotic pressure gradient. In the FO process, a semi-permeable membrane separates twodue solutions osmotic pressure gradient [14]. We will highlight that, beyond a certain water review, discuss the challenges of FO evidences from various literatures to prove the unreliability of permeability, the true bottleneck is the mechanical support of the membrane instead of the selective the existing structural parameter approaches. There is a of common that one of the advantages of FO over pressure-driven membrane
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