Facile development of comprehensively fouling-resistant reduced polyketone-based thin film composite forward osmosis membrane for treatment of oily wastewater

Resilient forward osmosis membranes against microplastics fouling enhanced by MWCNTs/UiO-66-NH2 hybrid nanoparticles

The escalating presence of microplastics (MPs) in wastewater necessitates the investigation of effective tertiary treatment process. Forward osmosis (FO) emerges as an effective non-pressurized membrane process, however, for the effective implementation of FO systems, the development of fouling-resistance FO membranes with high-performance is essential. This study focuses on the integration of MWCNT/UiO-66-NH2 as metal-organic frameworks (MOFs) and multi-wall carbon nanotubes (MWCNT) nanocomposites in thin film composite (TFC) FO membranes, harnessing the synergistic power of hybrid nanoparticles in FO membranes. The results showed that the addition of MWCNT/UiO-66-NH2 in the aqueous phase during polyamide formation changed the polyamide surface structure, and enhanced membranes' hydrophilicity by 44%. The water flux of the modified FO membrane incorporated with 0.1 wt% MWCNTs/UiO-66-NH2 increased by 67% and the reverse salt flux decreased by 22% as in comparison with the control membrane. Moreover, the modified membrane showed improved antifouling behavior against both organic foulant and MPs. The MWCNT/UiO-66-NH2 membrane experienced 35% flux decline while the control membrane experienced 65% flux decline. This proves that the integration of MWCNT/UiO-66-NH2 nanoparticles into TFC FO membranes is a viable approach in creating advanced FO membranes with high antifouling propensity with potential to be expanded further to other membrane applications.

Strategies to improve membrane performance in wastewater treatment

Membrane technology has rapidly gained popularity in wastewater treatment due to its cost-effectiveness, environmentally friendly tools, and elevated productivity. Although membrane performance in wastewater treatment has been reviewed in several past studies, the key techniques for improving membrane performance, as well as their challenges, and solutions associated with the membrane process, were not sufficiently highlighted in those studies. Also, very few studies have addressed hybrid techniques to improve membrane performance. The present review aims to fill those gaps and achieve public health benefits through safe water processing. Despite its higher cost, membrane performance can result in a 36% reduction in flux degradation. The issue with fouling has been identified as one of the key challenges of membrane technology. Chemical cleaning is quite effective in removing accumulated foulant. Fouling mitigation techniques have also been shown to have a positive effect on membrane photobioreactors that handle wastewater effluent, resulting in a 50% and 60% reduction in fouling rates for backwash and nitrogen bubble scouring techniques. Membrane hybrid approaches such as hybrid forward-reverse osmosis show promise in removing high concentrations of phosphorus, ammonium, and salt from wastewater. The incorporation of the forward osmosis process can reject 99% of phosphorus and 97% of ammonium, and the reverse osmosis approach can achieve a 99% salt rejection rate. The control strategies for membrane fouling have not been successfully optimized yet and more research is needed to achieve a realistic, long-term direct membrane filtering operation.

Developing a Thin Film Composite Membrane with Hydrophilic Sulfonated Substrate on Nonwoven Backing Fabric Support for Forward Osmosis

This study describes the fabrication of sulfonated polyethersulfone (SPES) as a super-hydrophilic substrate for developing a composite forward osmosis (FO) membrane on a nonwoven backing fabric support. SPES was prepared through an indirect sulfonation procedure and then blended with PES at a certain ratio. Applying SPES as the substrate affected membrane properties, such as porosity, total thickness, morphology, and hydrophilicity. The PES-based FO membrane with a finger-like structure had lower performance in comparison with the SPES based FO membrane having a sponge-like structure. The finger-like morphology changed to a sponge-like morphology with the increase in the SPES concentration. The FO membrane based on a more hydrophilic substrate via sulfonation had a sponge morphology and showed better water flux results. Water flux of 26.1 L m⁻² h⁻¹ and specific reverse solute flux of 0.66 g L⁻¹ were attained at a SPES blend ratio of 50 wt % when 3 M NaCl was used as the draw solution and DI water as feed solution under the FO mode. This work offers significant insights into understanding the factors affecting FO membrane performance, such as porosity and functionality.

Molecular dynamics study on the elucidation of polyamide membrane fouling by nonionic surfactants and disaccharides

Reverse osmosis (RO) is a widely used energy-efficient separation technology for water treatment. Polyamide (PA) membranes are the conventional choice for this process. Fouling is a serious problem for RO separation. This issue leads to significant decreases in the water permeability of PA membranes, and it has yet to be fully elucidated. In particular, the fouling behavior of a nonionic substance on the negatively charged surface of a PA membrane in an aqueous environment has not been previously studied. In this work, the mechanisms of nonionic substances such as polyoxyethylene octyl ether (PE5) and maltose (Mal) were investigated using molecular dynamics (MD) simulations. In a PA membrane in which the carboxyl group was not dissociated, the hydrophobic portion of the membrane was exposed due to the localization of water molecules around the carboxyl groups in the PA membrane. This caused hydrophobic interaction with the hydrophobic groups of PE5. In the case of an amine-modified PA membrane containing no carboxyl groups, water was not localized around the functional group, and the water orientation of the polyamide surface was also low. Due to this membrane property, the presence of stabilized water around PE5 reduced the number of hydrophobic interactions. In similar manner, a PA membrane with a slightly dissociated carboxyl group was hydrophilic, which reduced the PE5 adsorption. The presence of many dissociated carboxyl groups, however, enhanced the adsorption of PE5 due to the increase in interactions between the dissociated carboxyl groups and the hydrophilic groups of PE5. Therefore, PE5 exhibited an amphipathic adsorption wherein both hydrophilic and hydrophobic groups contributed to adsorption onto the PA membrane. Mal, on the other hand, was highly stable in every aqueous environment independent of the state of the functional groups of the PA membrane, and was not easily affected by the properties of the PA membrane.