Forward Osmosis Membrane: Review of Fabrication, Modification, Challenges and Potential

Abstract

Forward osmosis (FO) is a low-energy treatment process driven by osmosis to induce the separation of water from dissolved solutes/foulants through the membrane in hydraulic pressure absence while retaining all of these materials on the other side. All these advantages make it an alternative process to reduce the disadvantages of traditional desalination processes. However, several critical fundamentals still require more attention for understanding them, most notably the synthesis of novel membranes that offer a support layer with high flux and an active layer with high water permeability and solute rejection from both solutions at the same time, and a novel draw solution which provides low solute flux, high water flux, and easy regeneration. This work reviews the fundamentals controlling the FO process performance such as the role of the active layer and substrate and advances in the modification of FO membranes utilizing nanomaterials. Then, other aspects that affect the performance of FO are further summarized, including types of draw solutions and the role of operating conditions. Finally, challenges associated with the FO process, such as concentration polarization (CP), membrane fouling, and reverse solute diffusion (RSD) were analyzed by defining their causes and how to mitigate them. Moreover, factors affecting the energy consumption of the FO system were discussed and compared with reverse osmosis (RO). This review will provide in-depth details about FO technology, the issues it faces, and potential solutions to those issues to help the scientific researcher facilitate a full understanding of FO technology.

Keywords: FO application; draw solution; energy consumption; forward osmosis; nanoparticles; operating conditions; thin film composite membrane; thin film nanocomposite membrane.

Figure 1

Information about global water and global supply and use of freshwater according to UN-Water “everythingconnects.org/fresh-water (accessed on 25 December 2022)”.

Figure 2

FO publications growth since 2010. The information was obtained from Science Direct using “forward osmosis” as a keyword.

Figure 3

Schematic diagram of a FO process concept.

Figure 4

Scanning electron microscopy (SEM) images of the cross-section of the TFC membrane prepared at various MPD concentrations (TMC concentration is fixed at 0.1%). (a) 0.1%, (b) 0.2%, (c) 1%, (d) 2%, (e) 4%, (f) 20%. Reproduced from reference [60] with permission from Elsevier (2017).

Figure 5

Scanning electron microscopy (SEM) images of the cross-section of the TFC membrane prepared at various TMC concentrations (MPD concentration is fixed at 2%). (a) 0.01%, (b) 0.05%, (c) 0.1%, (d) 0.2%, (e) 1%. Reproduced from reference [60] with permission from Elsevier (2017).

Figure 6

Scanning electron microscopy (SEM) images of the cross-section and top surface of PSF substrates prepared from different TiO₂ nanoparticles loading, (a) PSf, (b) PSf 0.30, (c) PSf 0.60, and (d) PSf 0.90 substrate. Reproduced from reference [75] with permission from Elsevier (2014).

Figure 7

Scanning electron microscopy (SEM) pictures of the cross-section and top surface of support layers with various ZnO@PMMA loading (0, 0.125, 0.25, and 0.5 wt.%) Reproduced from reference [83] with permission from Elsevier (2022).

Figure 8

Normalized FO seawater flux decline of the membranes over 1-day (FS/Caspian seawater, DS/2 M NaCl, T/25 °C, Mode/AL-FS). Reproduced from reference [42] with permission from Elsevier (2017).

Figure 9

(a) Transmission electron microscopy (TEM) pictures of TiO₂ and GO nanomaterial; (b) Scanning electron microscopy (SEM) pictures of a substrate (control) and substrate (TiO₂/GO). Reproduced from reference [86] with permission from Elsevier (2017).

Figure 10

Some important characteristics of an ideal draw solution (DS).

Figure 11

Effect increasing of operating conditions for feed solution (FS) or draw solution (DS) on FO performance.

Figure 12

Schematic descriptions of ECP and ICP at AL–FS orientation (left-hand side figure) and AL–DS orientation (right-hand side figure).

Figure 13

Schematic descriptions of membrane fouling at AL–FS orientation (left-hand side figure) and AL–DS orientation (right-hand side figure).

Figure 14

The effect of p-TiO₂ [46], GO [69], SiO₂ [81], Fe₃O₄/ZnO [89], TiO₂/HNTs [94], GO/Fe₃O₄ [100], TiO₂ [161], and GO [162] on various foulants of the composite membrane in FO mode.

Figure 15

The effect of temperature [142], cross-flow velocity [143], DS concentration [143], membrane orientation [148], FS type [155,156], FS concentration [163], and DS type [164] on membrane fouling.