Improved antifouling performance of a polyamide composite reverse osmosis membrane by surface grafting of dialdehyde carboxymethyl cellulose (DACMC)

A review on antifouling polyamide reverse osmosis membrane for seawater desalination

Reverse osmosis (RO) membrane technology is well-established in desalination. Aromatic polyamide (PA) thin-film composite (TFC) membrane dominates the commercial RO membrane market due to its high-salt rejection, water flux, and excellent chemical, thermal, and mechanical stabilization. However, membrane fouling is a common problem that has seriously hindered the wide application of RO membrane technology. This paper reviewed the PA RO membrane fouling types, and membrane fouling factors. Antifouling measures for RO membranes were summarized, including pretreatment, periodic cleaning, and modification of the support layer and PA layer. The future development of antifouling RO membranes was clarified.

Construction of a Covalent Crosslinked Membrane Exhibiting Superhydrophilicity and Underwater Superoleophobicity for the Efficient Separation of High-Viscosity Oil-Water Emulsion Under Gravity

The separation of high-viscosity oil-water emulsions remains a global challenge due to ultra-stable interfaces and severe membrane fouling. In this paper, SiO2 micro-nanoparticles coated with polyethyleneimine (PEI) were initially loaded onto a stainless steel substrate. This dual-functional design simultaneously modifies surface roughness and wettability. Furthermore, a covalent crosslinking network was created through the Schiff base reaction between PEI and glutaraldehyde (GA) to enhance the stability of the membrane. The membrane exhibits extreme wettability, superhydrophilicity (WCA = 0°), and underwater superoleophobicity (UWOCA = 156.9°), enabling a gravity-driven separation of pump oil emulsions with 99.9% efficiency and a flux of 1006 L·m-2·h-1. Moreover, molecular dynamics (MD) simulations demonstrate that the SiO2-PEI-GA-modified membrane promotes the formation of a stable hydration layer, reduces the oil-layer interaction energy by 85.54%, and exhibits superior underwater oleophobicity compared to the unmodified SSM. Efficiency is maintained at 99.8% after 10 cycles. This study provides a scalable strategy that combines covalent crosslinking with hydrophilic particle modification, effectively addressing the trade-off between separation performance and membrane longevity in the treatment of viscous emulsions.

Fouling of Reverse Osmosis (RO) and Nanofiltration (NF) Membranes by Low Molecular Weight Organic Compounds (LMWOCs), Part 1: Fundamentals and Mechanism

Reverse osmosis (RO) and nanofiltration (NF) are ubiquitous technologies in modern water treatment, finding applications across various sectors. However, the availability of high-quality water suitable for RO/NF feed is diminishing due to droughts caused by global warming, increasing demand, and water pollution. As concerns grow over the depletion of precious freshwater resources, a global movement is gaining momentum to utilize previously overlooked or challenging water sources, collectively known as "marginal water". Fouling is a serious concern when treating marginal water. In RO/NF, biofouling, organic and colloidal fouling, and scaling are particularly problematic. Of these, organic fouling, along with biofouling, has been considered difficult to manage. The major organic foulants studied are natural organic matter (NOM) for surface water and groundwater and effluent organic matter (EfOM) for municipal wastewater reuse. Polymeric substances such as sodium alginate, humic acid, and proteins have been used as model substances of EfOM. Fouling by low molecular weight organic compounds (LMWOCs) such as surfactants, phenolics, and plasticizers is known, but there have been few comprehensive reports. This review aims to shed light on fouling behavior by LMWOCs and its mechanism. LMWOC foulants reported so far are summarized, and the role of LMWOCs is also outlined for other polymeric membranes, e.g., UF, gas separation membranes, etc. Regarding the mechanism of fouling, it is explained that the fouling is caused by the strong interaction between LMWOC and the membrane, which causes the water permeation to be hindered by LMWOCs adsorbed on the membrane surface (surface fouling) and sorbed inside the membrane pores (internal fouling). Adsorption amounts and flow loss caused by the LMWOC fouling were well correlated with the octanol-water partition coefficient (log P). In part 2, countermeasures to solve this problem and applications using the LMWOCs will be outlined.

Improving multifunctional properties of the polyvinylidene fluoride (PVDF) membrane with crosslinked dialdehyde-starch (DAS) and polyethyleneimine (PEI) coating

Dialdehyde-soluble starch (DAS) and polyethyleneimine (PEI) were used to coat the polyvinylidene fluoride (PVDF) membrane for improving its antifouling and multifunctional properties through a combination of dip-coating and spray-coating techniques. The resulting membrane demonstrated excellent hydrophilicity and underwater oleophobicity due to hydrophilic DAS and PEI on its surface. The membrane achieved an impressive oil removal rate of 99.8 % and a flux 1420.8 ± 26.5 L·m-2·h-1 when it was used for oil-water emulsion separation. The hydration layer formed by the DAS and PEI greatly enhanced the membrane antifouling property, and its flux recovery rate was up to 96.6 % in BSA filtration experiments. The positive charge PEI and the negative charge DAS contributed to high separation efficiency of 99.1 % for the anion dye MO with the membrane D10P20, and high separation efficiency of 88.3 % for the cation dye RhB with the membrane P5D20. In addition, the coating layer was stable due to the cross-linked DAS and PEI. This research contributes greatly to the preparation of antifouling and multifunctional membrane using environmentally friendly material including polysaccharide derivatives and water soluble polymer.

Designing sustainable membrane-based water treatment via fouling control through membrane interface engineering and process developments

Membrane-based water treatment processes have been established as a powerful approach for clean water production. However, despite the significant advances made in terms of rejection and flux, provision of sustainable and energy-efficient water production is restricted by the inevitable issue of membrane fouling, known to be the major contributor to the elevated operating costs due to frequent chemical cleaning, increased transmembrane resistance, and deterioration of permeate flux. This review provides an overview of fouling control strategies in different membrane processes, such as microfiltration, ultrafiltration, membrane bioreactors, and desalination via reverse osmosis and forward osmosis. Insights into the recent advancements are discussed and efforts made in terms of membrane development, modules arrangement, process optimization, feed pretreatment, and fouling monitoring are highlighted to evaluate their overall impact in energy- and cost-effective water treatment. Major findings in four key aspects are presented, including membrane surface modification, modules design, process integration, and fouling monitoring. Among the above mentioned anti-fouling strategies, a large part of research has been focused on membrane surface modifications using a number of anti-fouling materials whereas much less research has been devoted to membrane module advancements and in-situ fouling monitoring and control. At the end, a critical analysis is provided for each anti-fouling strategy and a rationale framework is provided for design of efficient membranes and process for water treatment.

Enhanced tetracycline removal using membrane-like air-cathode with high flux and anti-fouling performance in flow-through electro-filtration system

The membrane-like air-cathodes modified with different polyaniline were prepared using phase inversion method, which possessed dual functions of interception and electrochemical degradation, and showed good conductivity (15.9 ± 0.4 to 25.7 ± 0.5 mS cm^-1) and porosity (77.0 ± 0.1 to 87.8 ± 0.1%) compared to the unmodified control one (13.2 ± 0.5 mS cm^-1, and 63.1 ± 0.7%). At tetracycline 50 mg L^-1, the cathode with 25 wt% polyaniline exhibited the highest rejection rate and final removal (71.1% and 92.9%, 35.9% and 31.4% higher than the control), the highest water flux recovery (97.9%), and the lowest attenuation of porosity and conductivity. The modified cathode also showed an autocatalytic effect on H₂O₂, an obvious ^·OH peak appeared on the electron paramagnetic resonance curves. It also had good anti-fouling performance because it exhibited a high durability (the final removal was decreased by 4.0% after 15 cycles) with a long service life of 124 periods (372 h, 15.5 d). The tetracycline (0.5 mg L^-1) removal in the river background was near 100%, and the chemical oxygen demand removal was 91.9%, supporting that it was suitable for treating antibiotics in natural water without adding agents but only for electricity consumption.

Surface modification of commercial reverse osmosis membranes using both hydrophilic polymer and graphene oxide to improve desalination efficiency

Various methods have been applied to modify the surface of reverse osmosis (RO) membranes to modify the membrane performance to enhance the flux, rejection, and resistance to various factors of fouling. Hence, the main objective of the current study is to modify the surface of commercial RO membranes using the synergistic effect of the hydrophilic polymer and graphene oxide (GO). GO nanosheets were firstly synthesized by the modified hummer method, then characterized by FTIR, XRD, and SEM analyses. Then, the polyacrylic acid (PAA) was grafted on the membrane surface for membrane fabrication. Furthermore, effective factors of grafting such as monomer concentration, time, and temperature of polymerization were optimized. After that, different amounts of GO nanosheets were loaded in PAA optimized layer. Then, the effect of GO loading on the RO membrane structure and performance was investigated. The outcomes of membrane characterization demonstrated that modified RO membranes had a smoother surface, more negative surface charge, a little better hydrophilicity, and more thickness. Moreover, the results of PAA and GO optimization were shown that grafting 1.5 mM of PAA and loading 0.1 wt% of GO nanosheets give the best membrane performance. This membrane (GO 0.1@1.5M PAA/RO) between all modified membranes has the most water flux (37.1 L/m²h), the highest NaCl rejection (98%), and the best antifouling efficiency. Ultimately, it was concluded that the grafting of GO@PAA on the surface of a commercial RO membrane is an efficient approach for the enhancement of desalination and antifouling performance of this kind of membrane.

A critical review on diverse technologies for advanced wastewater treatment during SARS-CoV-2 pandemic: What do we know?

Advanced wastewater treatment technologies are effective methods and currently attract growing attention, especially in arid and semi-arid areas, for reusing water, reducing water pollution, and explicitly declining, inactivating, or removing SARS-CoV-2. Overall, removing organic matter and micropollutants prior to wastewater reuse is critical, considering that water reclamation can help provide a crop irrigation system and domestic purified water. Advanced wastewater treatment processes are highly recommended for contaminants such as monovalent ions from an abiotic source and SARS-CoV-2 from an abiotic source. This work introduces the fundamental knowledge of various methods in advanced water treatment, including membranes, filtration, Ultraviolet (UV) irradiation, ozonation, chlorination, advanced oxidation processes, activated carbon (AC), and algae. Following that, an analysis of each process for organic matter removal and mitigation or prevention of SARS-CoV-2 contamination is discussed. Next, a comprehensive overview of recent advances and breakthroughs is provided for each technology. Finally, the advantages and disadvantages of each method are discussed.

Biomolecule-Enabled Liquid Separation Membranes: Potential and Recent Progress

The implementation of membrane surface modification to enhance the performance of membrane-based separation has become a favored strategy due to its promise to address the trade-off between water permeability and salt rejection as well as to improve the durability of the membranes. Tremendous work has been committed to modifying polymeric membranes through physical approaches such as surface coating and ontology doping, as well as chemical approaches such as surface grafting to introduce various functional groups to the membrane. In the context of liquid separation membranes applied for desalination and water and wastewater treatment, biomolecules have gained increasing attention as membrane-modifying agents due to their intriguing structural properties and chemical functionalities. Biomolecules, especially carbohydrates and proteins, exhibit attractive features, including high surface hydrophilicity and zwitterionic and antimicrobial properties that are desired for liquid separation membranes. In this review, we provide an overview of the recent developments in biomolecule-enabled liquid separation membranes. The roles and potentials of some commonly explored biomolecules in heightening the performance of polymeric membranes are discussed. With the advancements in material synthesis and the need to answer the call for more sustainable materials, biomolecules could serve as attractive alternatives for the development of high-performance composite membranes.

Construction of antifouling zwitterionic membranes by facile multi-step integration method

Membrane fouling during the use of separation membrane has always been the main reason for the degradation of membrane performance. The traditional solution is complicated and inefficient, so we proposed multi-step integration method to prepare antifouling zwitterionic poly(aryl ether sulfone) (PAES-Z-x) ultrafiltration (UF) membrane with higher efficiency. We designed and synthesized a bisphenol precursor containing tertiary amine groups, which could provide reactive sites for grafting zwitterionic group. Afterwards, the zwitterionic modified UF membrane was prepared by graft copolymerization and non-solvent-induced phase separation (NIPS). The morphology, hydrophilicity, water flux and rejection of the PAES-Z-x membrane could be optimized by tuning zwitterion content. The hydration layer formed by zwitterions effectively reduced the adsorption of proteins and endowed the membrane good antifouling properties. The resulting membrane showed the pure water flux increased (up to 311 L m^-2h^-1 bar^-1), high bovine serum albumin (BSA) rejection (97%) and good water flux recovery ratio (FRR) (82.8%). Zwitterionic antifouling PAES UF membrane prepared by a simple and effective method provided a new direction for improving PAES UF membrane's antifouling performance.