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This study explored the impact of eco-friendly polydopamine (PDA) coated ZnFe2O4 nanocomposites (PDA@ZnFe2O4 NCs) as nanofillers to fabricate a new class of polyethersulfone (PES) hybrid ultrafiltration (UF) membranes for wastewater treatment applications. The hybrid UF membrane was prepared by incorporating PDA@ZnFe2O4 NCs into PES via the non-solvent induced phase separation (NIPS) process. The PDA@ZnFe2O4 NC was characterized by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Additionally, the morphology and performance of the prepared hybrid membranes were characterized by SEM, contact angle, surface charge, and thermogravimetric analysis (TGA). The incorporation of PDA@ZnFe2O4 NC into the PES membrane affects the porosity, mean pore radius, hydrophilicity, and thermal stability of the developed hybrid membranes. The pure water flux of the PES hybrid membrane with 4 wt% PDA@ZnFe2O4 reached ∼687 L/m2 h, which is about 188% higher than that of the pristine PES membrane. The performance of the PES/ PDA@ZnFe2O4ultrafiltration hybrid membrane was also investigated using humic acid (HA) foulant and oil/water emulsion individually. Compared to the pristine PES and PES/ZnFe2O4 membranes, the developed hybrid membranes showed enhanced permeability and HA foulant removal. HA's removal efficiency has improved from ∼65% in the pristine PES membrane to ∼94% in the 4 wt% PDA@ZnFe2O4 hybrid membrane. The abundant functional groups on the PDA@ZnFe2O4 NC surface also enhanced the separation of the oil/water emulsion (96%). In both the HA and oil/water emulsion separation tests, the flux recovery ratio (FRR) and reversible fouling ratio (Rr) were also significantly improved, suggesting that the PES/PDA@ZnFe2O4 membrane was a very promising candidate for HA removal and treatment of oily wastewater.

Nanomodification of ultrafiltration (UF) membranes has been shown to be a simple and efficient technique for the preparation of high-performance membranes. In this work, an iron oxide functionalized halloysite nanoclay (Fe-HNC) nanocomposite was prepared and used as a nanofiller for polyethersulfone (PES) membranes. The effect of Fe-HNC concentration on the filtration performance of the membrane was investigated by varying the nanocomposite dosage (0–0.5 wt. %) in the casting dope. Various characterization studies showed that the incorporation of Fe-HNC nanocomposites improved the membrane morphology and enhanced the surface properties, thermal stability, mechanical strength, hydrophilicity, and porosity. The permeability to pure water and filtration of humic acid (HA) were significantly improved by incorporating Fe-HNC into the PES membranes. The membrane with Fe-HNC loading of 0.1 wt. % exhibited the highest pure water permeability (174.3 L/m2 h bar) and removal of HA (90.1 %), which were 1.8 times and 29 % higher, respectively than the pristine PES membrane. Moreover, fouling studies showed the enhanced antifouling ability of the Fe-HNC nanocomposites modified PES membranes, especially against irreversible fouling. Continuous membrane regeneration-based fouling removal studies from HA showed that the PES/0.1 wt. % Fe-HNC membrane exhibited a high fouling recovery of 70.4 % with very low reversible and irreversible fouling resistance of 9.61 % and 14.78 %, respectively, compared to the pristine PES membrane (fouling recovery: 40.4 %; reversible fouling: 21.7 %; irreversible fouling: 20.1 %). Overall, the Fe-HNC nanocomposite proved to be an effective nanomodifier for improving the permeability of PES membranes and the antifouling ability to treat HA polluted aqueous streams.

Membrane-based technologies are vital in water purification processes such as desalination and wastewater recycling. Polymeric membranes dominate the membrane market; however, they still suffer from issues related to their chemical, mechanical, and thermal stability, and more importantly, membrane fouling. However, these membranes are associated with various environmental problems that occur during their production and disposal. In this work, an eco-friendly and biodegradable membrane composed of polylactic acid (PLA), hydroxyapatite (HAp) as filler, and polydopamine (PDA) as surface coating was proposed. This unique combination and synergic effect of HAp and PDA were found to enhance the PLA membrane's permeation notably. The fabricated PLA/HAp/PDA membrane resulted in an increase in water permeability of the pristine PLA membrane from 359 ± 76 L/m2.h.bar to 788 ± 58 L/m2.h.bar for the membrane coated with 2 wt.% HAp/1-hour PDA (PLA-H/PDA-1). Similarly, the flux recovery ratio (FRR) increased from 20% for the pristine PLA membrane to 54% for the PLA-H/PDA-1 membrane after 3 cycles. These properties were found to be due to the enhanced membrane characteristics. For instance, the contact angle dropped by 5% (i.e., the membrane became more hydrophilic) and the porosity increased from 55 to 60%. The pore size was also increased from 97 to 133 nm as a result. The modified membranes retained up to 87% of the normal organic matter (NOM), and no deterioration in the thermal properties of the membranes was observed. These membranes open a new route to a circular economy in membrane technology by reducing environmental costs while allowing continuous operation of the membranes.

This study presents the synthesis of a novel graphene oxide-manganese oxide (GO-MnO2) nanohybrid and its incorporation into sulfonated polyethersulfone (SPES) ultrafiltration (UF) membranes for wastewater treatment applications. The nanohybrid was first prepared by grafting ethylenediamine (ED) onto the edge of GO followed by direct mixing with the MnO2 nanosheets. The composite membranes were prepared via the phase inversion method and optimized by varying the concentration of the GO-MnO2 nanohybrid (0–6 wt%). The membranes were characterized using scanning electron microscopy, surface zeta potential, water flux, porosity, among others. The results showed that the pure water flux increased from 59.5 ± 2.5 L·m−2·h−1 in the pristine SPES membrane to 129.7 ± 4.1 L·m−2·h−1 in the SPGM4 (4 wt% GO-MnO2). Furthermore, the heavy metal ions rejection improved from 70.1, 49.1, and 55.8% for Cu2+, Zn2+, and Ni2+ ions, respectively, in the pristine SPES membrane to 81.1, 64.0, and 67.4% in the SPGM4 membrane. Also, the composite membranes revealed improvement in the anti-fouling properties over the pristine SPES membrane. For example, the SPGM4 membrane recovered 90.5 ± 2.9% of its initial flux compared to only 72.6 ± 3.1% in the pristine membrane after 4 cycles of heavy metal filtration and simple acid cleaning steps. Overall, the addition of GO-MnO2 nanohybrid enhanced the properties of the pristine SPES, creating new potential for such composite membranes in the wastewater treatment industry.

Oily wastewater is the largest liquid waste generated, mainly resulting from oil and gas production. It consists of hazardous materials, salts, toxic chemicals, surfactants and crude oil content. Therefore, it is considered a huge threat for the environment and marine life, and hence needs to be adequately treated before discharge into the sea. Among all technologies used for oily wastewater treatment, membrane technology has been found to be effective in handling emulsified oil droplets with a particle size of less than 40 μm. However, one of the major obstacles associated with the membrane technology is the deposition of foulants onto the membrane surface, a phenomenon referred to as membrane fouling, which severely reduces the treatment efficiency. Oily wastewater is an aggressive environment; hence membrane fouling could hugely and adversely impact the membrane performance. Recently, membrane fouling mitigation has been a main focus for researchers working in the area. In this review, various membrane fouling mitigation techniques in the treatment of oily wastewater were assessed. Membrane oscillation and pore structure, for example, play an important role in membrane fouling mitigation and have not been reviewed in the literature. The present study is mainly focused on the latest published literature in the field of fouling mitigation techniques for oily wastewater. It was found that membrane surface modification, chemical cleaning, membrane oscillation, pore structure, back flushing, and ultrasound are among the most common methods used for fouling mitigation. Therefore, these technologies were studied in detail and their limitations were reflected upon. Finally, the current status of these technologies was studied, and future trends were drawn out.

In this study, phase-inverted polyethersulfone (PES)-maghemite (γ-Fe2O3) composite membranes were fabricated and tested for oil-water separation. The performance of five different composite membranes with various loadings of γ-Fe2O3 (0.25, 0.50, 0.75, and 1.00 wt.%) in terms of water flux, flux recovery, and oil rejection was investigated. The surface morphology, crystallinity, and functionalities of the membranes were characterized via scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and Fourier-transform infrared (FT-IR). Furthermore, the porosity, pore size, water contact angle, and underwater oil contact angle of the composite membranes were examined. Results showed that the pristine PES membrane reported a pure water flux of 1242 ± 12 L/m2h (LMH) compared to 1323 ± 27 LMH for the 0.25 wt.% PES/γ-Fe2O3 membrane. Additionally, 56 and 23 % flux recovery ratio (FRR) were reported for the PES/γ-Fe2O3 and the pristine PES membrane, respectively. Also, the removal efficiency has increased from 39.2 % in the PES membrane to 81.7 % in the 1.00 wt.% PES/γ-Fe2O3 composite membrane. Two phenomena played a role in the removal trends, namely size exclusion and electrostatic repulsion forces. The developed membranes exhibited significant application potential for the removal of oil from wastewater.