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Hazardous micropollutants (MPs) such as pharmaceutically active compounds (PhACs), pesticides and personal care products (PCPs) have emerged as a critical concern nowadays for acquiring clean and safe water resources. In the last few decades, innumerable water treatment methods involving biodegradation, adsorption and advanced oxidation process have been utilized for the removal of MPs. Of these methods, membrane technology has proven to be a promising technique for the removal of MPs due to its sustainability, high efficiency and cost-effectiveness. Herein, the aim of this article is to provide a comprehensive review regarding the MPs rejection mechanisms of reverse osmosis (RO) and nanofiltration (NF) membranes after incorporation of nanomaterials and also surface modification atop the PA layer. Size exclusion, adsorption and electrostatic charge interaction mechanisms play important roles in governing the MP removal rate. In addition, this review also discusses the state-of-the-art research on the surface modification of thin film composite (TFC) membrane and nanomaterials-incorporated thin film nanocomposite (TFN) membrane in enhancing MPs removal performance. It is hoped that this review can provide insights in modifying the physicochemical properties of NF and RO membranes to achieve better performance in water treatment process, particularly for the removal of emerging hazardous substances. Schematic illustration of surface-modified TFC membrane and nanomaterials-incorporated TFN membrane against MPs compounds. [Display omitted] • Occurrence, risks and type of emerging micropollutants (MPs) have been identified. • Removal of emerging MPs via RO and NF membranes have been summarized. • TFN and surface-modified TFC membranes showed remarkable MPs removal rate. • The MPs rejection mechanisms of polyamide RO/NF membranes were elucidated. [ABSTRACT FROM AUTHOR]

Due to the continuing growth of reverse osmosis (RO) water treatment plants worldwide, the amount of discarded end-of-life (EoL) RO membrane modules is expected to increase drastically in coming years. One of the approaches to address this problem is to transform the EoL membranes for other purposes. In this study, a new approach based on sonication was studied to convert the EoL RO membrane from RO properties into microfiltration (MF) properties, offering a transformation process that was much faster (15 min) than that of typical chemical treatment process (ranging from hours to days) using oxidizing agent solution. Our results indicated that with only 15-min ultrasonication, the properties of EoL RO membrane could be significantly altered, reaching pure water permeability of 172.6 L/m2.h.bar (70-fold increment) with NaCl rejection reduced from ~80% to less than 2%. This is attributed to the deterioration of the polyamide thin selective layer atop the EoL RO membrane. As a comparison, the chemical treatment using 5000-ppm potassium permanganate (KMnO 4) solution requires at least 168 h to achieve similar membrane properties. It was also found that the presence of KMnO 4 during ultrasonication process could accelerate the rate of polymeric degradation, resulting in even higher pure water permeation. As a conclusion, our work demonstrated a rapid and new approach that is capable of transforming the EoL RO membrane for the filtration process of macromolecules, thus offering a practical solution to address the disposal issues of EoL RO membrane modules. [Display omitted] • A new approach based on sonication method to convert discarded RO membrane to MF application. • Ultrasonication method is able to convert RO membrane into MF membrane within a short time (15 min). • Soni/KMnO 4 -treated membrane exhibited remarkable HA separation (~ 82%). [ABSTRACT FROM AUTHOR]

Membrane surface scaling is a major challenge in reverse osmosis (RO) desalination process that could irreversibly deteriorate the membrane filtration efficiency. In this study, a hydrophilic coating layer was introduced onto the polyamide (PA) layer of self-developed thin film nanocomposite (TFN) membrane via plasma enhanced chemical vapour deposition (PECVD) technique to increase the membrane surface energy barrier and hydrophilicity towards silica heterogeneous nucleation. The results revealed that the acrylic acid-coated TFN membrane (AA-TFN) exhibited excellent resistance against silica scaling after subjected to saturated silica concentration (168 ppm at pH 6.7), with much higher flux recovery rate (FRR) (88%) compared to the uncoated TFN (75.5%) and conventional thin film composite (TFC) (72%) membranes. This is attributed to its enhanced surface hydrophilicity (contact angle of 26°) and better surface charge (zeta potential of −47 mV at pH 6.7) upon the hydrophilic coating layer deposition which retards the scale deposition. The membrane scaling can be further reduced by increasing the feed pH and at the optimized condition (pH 10), the FRR of AA-TFN membrane could reach up to 98.3%, owing to the increased silica solubility at alkaline condition which minimizes the silica aggregation formation on the membrane surface. Our work demonstrated that surface modification of composite membrane using suitable materials and proper feed pH adjustment could offer a great promise in mitigating the scaling for desalination applications. The findings also provide fundamental insights on the importance of membrane surface properties during silica scaling formation. Schematic illustration of scaling mechanism on membrane [Display omitted] • Rapid and eco-friendly method for surface modification of TFN membrane • Silica feed solution at pH 10 can effectively reduce silica aggregation tendency. • AA-TFN membrane with higher surface negative charge at pH 10 achieves better FRR (98.3%). [ABSTRACT FROM AUTHOR]

In this work, an environmentally friendly plasma enhanced chemical vapor deposition (PECVD) technique was employed to rapidly alter the surface properties of commercial thin film composite extra-low energy (XLE) reverse osmosis (RO) membrane to improve its fouling resistance and desalination performance. Hereafter, two different hydrophilic precursors, i.e., aniline monomer and oxygen (O 2) gas were respectively introduced to the membrane's polyamide surface at different plasma treatment duration (15 s and 60 s). At 15-s plasma treatment, our results revealed that the O 2 -modified membrane outperformed the polyaniline (PANI)-modified membrane and unmodified membrane, attributed to the polar functional groups presented on the polyamide surface. Compared to plasma polymerization of aniline, O 2 plasma etching can lower polyamide densification degree which potentially reduce membrane resistance. Evidently, the O 2 -modified membrane exhibited higher pure water permeability (6.64 L/m2.h.bar) compared to the PANI-modified membrane (5.57 L/m2.h.bar). The enhanced surface hydrophilicity of O 2 -modified membrane could be noticed when its water contact angle was reduced from 88.39⁰ (unmodified) to 79.46⁰ in just 15-s plasma treatment. Furthermore, this O 2 -modified membrane achieved an outstanding NaCl and Na 2 SO 4 rejection with an increment of 4.2% and 2.6%, respectively compared to the unmodified membrane. However, prolonged gas plasma treatment (60 s) should be avoided as it can damage polyamide selective layer. With respect to fouling resistance, the best O 2 -modified membrane demonstrated higher flux recovery rate (96%) than that of unmodified membrane (76.5%) after being used to filter 1000-ppm sodium alginate solution. These results highlighted the versatility of O 2 plasma treatment to improve RO membrane performance. Schematic illustration of (a,b) plasma gas treatment and plasma polymerization on the commercial extra-low energy (XLE) RO membrane surface using oxygen (O) and aniline (A), respectively and their properties with respect to (c) water contact angle and (d) normalized permeability [Display omitted] • Rapid and eco-friendly method for surface modification of commercial TFC RO membrane. • O 2 -modified XLE RO membrane showed outstanding antifouling property and FRR (>95%). • NaCl rejection of XLE RO membrane was elevated from 91.38% to 95.58% upon 15-s O 2 plasma treatment. [ABSTRACT FROM AUTHOR]