Defect-free outer-selective hollow fiber thin-film composite membranes for forward osmosis applications

Abstract

This study presents the successful fabrication of a novel defect-free outer-selective hollow fiber (OSHF) thin-film composite (TFC) membrane for forward osmosis (FO) applications. Thin and porous FO membrane substrates made of polyether sulfone (PES) with a dense and smooth outer surface were initially fabricated at different air-gap distances. A modified vacuum-assisted interfacial polymerisation (VAIP) technique was then successfully utilised for coating polyamide (PA) layer on the hollow fiber (HF) membrane substrate to prepare OSHF TFC membranes.Experimental results showed that the molecular weight cut-off (MWCO) of the surface of the membrane substrate should be less than 88 kDa with smooth surface roughness to obtain a defectfree PA layer via VAIP. The FO test results showed that the newly developed OSHF TFC membranes achieved water flux of 30.2 L m -2 h -1 and a specific reverse solute flux of 0.13 g L -1 using 1M NaCl and DI water as draw and feed solution, respectively. This is a significant improvement on commercial FO membranes. Moreover, this OSHF TFC FO membrane demonstrated higher fouling resistance and better cleaning efficiency against alginate-silica fouling. This membrane also has a strong potential for scale-up for use in larger applications. It also has strong promise for various FO applications such as osmotic membrane bioreactor (OMBR) and fertiliser-drawn OMBR processes.

Feasibility of using polycarbonate as a substrate of thin film composite membrane in forward osmosis

“…PVP 4,29–31 and PEG as pore former are the most widely used additives used in FO membranes synthesis. Although addition of hydrophilic PEG into the dope solutions can improve pore formation and interconnection by producing a sponge‐like porous morphology, 32 but our pre‐tests revealed that the membrane fabricated by PEG 400 and PC was mechanically too weak and powdery. As a result, in this study PVP was selected as pore former.…”

“…The pure water flux for the PC substrate was remarkably higher than that of the PES substrate. The pure water flux depends on the bulk porosity, surface porosity, and pore size due to the Hagen‐Poiseuille pore flow model 32 as well as the hydrophilicity of the substrates 27 . Water permeability and other characteristics of the substrates are also represented in Table 2.…”

“…2 Based on the water flux performance under the two modes, it can be concluded that, the type of the substrate indicated an important effect on the performances of the TFC-FO membranes in terms of water flux and reverse salt flux. Indeed, fabricating defectless with excellent performance is related to two factors of the substrate: (a) the hydrophilicity of substrate 49 and, (b) the membrane morphology, pore size, 32 and surface porosity. 15 Although the PWP of the PC membrane is higher than that of the PES membrane, the water flux in the forward osmosis process is lower for the polycarbonate membrane.…”

Cellulose Triacetate (CTA) Hollow-Fiber (HF) Membranes for Sustainable Seawater Desalination: A Review

“…In particular, the unique preparation procedure of PA-based membranes via interfacial polymerization on the porous support layer allows for a very thin selective layer formation, which results in much higher water permeability than the CTA-based membrane. On the other hand, at the same time, the two-step membrane preparation procedure of a PA-based membrane (porous support layer preparation and subsequent interfacial polymerization) might impede the mass production of the PA-based membrane applicable for the HF configuration, especially the outer-selective layer type of the PA-based membrane [ 67 ]. Although the CTA-based membrane has lower water permeability than the PA-based membrane, the simple preparation procedure of the CTA-based membrane allows for a HF configuration and a more highly effective membrane area compared to the PA-based membrane.…”

Membrane processes

“…It was found that VFA rejection by FO membrane was highly pH dependent and at pH 7.5 rejection rates above 80% was achievable. Lim, Tran, Tran, Akther, Phuntsho, and Shon (2019) successfully fabricated a defect-free outer-selective hollow fiber (OSHF) thin film composite (TFC) membrane for FO applications. This OSHF TFC membrane was found to achieve significant improvements on commercial FO membranes in water flux, specific reverse solute flux, fouling resistance, and cleaning efficiency.…”