Polyacrylic acid-brushes tethered to graphene oxide membrane coating for scaling and biofouling mitigation on reverse osmosis membranes

Graphene Oxide Surface Modification of Reverse Osmosis (RO) Membrane via Langmuir-Blodgett Technique: Balancing Performance and Antifouling Properties

The reverse osmosis water treatment process is prone to fouling issues, prompting the exploration of various membrane modification techniques to address this challenge. The primary objective of this study was to develop a precise method for modifying the surface of reverse osmosis membranes to enhance their antifouling properties. The Langmuir-Blodgett technique was employed to transfer aminated graphene oxide films assembled at the air-liquid interface, under specific surface pressure conditions, to the polyamide surface with pre-activated carboxylic groups. The microstructure and distribution of graphene oxide along the modified membrane were characterized using SEM, AFM, and Raman mapping techniques. Modification carried out at the optimal surface pressure value improved the membrane hydrophilicity and reduced the surface roughness, thereby enhancing the antifouling properties against colloidal fouling. The flux recovery ratio after modification increased from 65% to 87%, maintaining high permeability. The modified membranes exhibited superior performance compared to the unmodified membranes during long-term fouling tests. This membrane modification technique can be easily scaled using the roll-to-roll approach and requires minimal consumption of the modifier used.

Membrane modification with carbon nanomaterials for fouling mitigation: A review

This paper provides a comprehensive overview of recent advancements in membrane modification for fouling mitigation in various water treatment processes, employing carbon nanomaterials such as fullerenes, nanodiamonds, carbon quantum dots, carbon nanotubes, and graphene oxide. Currently, using different carbon nanomaterials for polymeric membrane fouling mitigation is at various stages: CNT-modified membranes have been studied for more than ten years and have already been tested in pilot-scale setups; tremendous attention has been paid to utilizing graphene oxide as a modifying agent, while the research on carbon quantum dots' influence on the membrane antifouling properties is in the early stages. Given the intricate nature of fouling as a colloidal phenomenon, the review initially delves into the factors influencing the fouling process and explores strategies to address it. The diverse chemistry and antibacterial properties of carbon nanomaterials make them valuable for mitigating scaling, colloidal, and biofouling. This review covers surface modification of existing membranes using different carbon materials, which can be implemented as a post-treatment procedure during membrane fabrication. Creating mixed-matrix membranes by incorporating carbon nanomaterials into the polymer matrix requires the development of new synthetic procedures. Additionally, it discusses promising strategies to actively suppress fouling through external influences on modified membranes. In the concluding section, the review compares the effectiveness of carbon materials of varying dimensions and identifies key characteristics influencing the antifouling properties of membranes modified with carbon nanomaterials.

Graphene Oxide Inhibits Calcium Carbonate Nucleation

Formation of minerals such as calcium carbonate often causes energy consumption and even safety risk increase due to the hindrance on heat/mass transfer. However, the current antiscalants are not efficient enough because of the poor understanding of the scale inhibition mechanisms. Here, we report an ultrahigh-performance antiscalant, graphene oxide (GO), which exhibits an outstanding nucleation inhibition effect far better than the current state-of-the-art antiscalants even on a subppm dosage. Our experiments reveal that the superior nucleation inhibition effect of GO is attributed to its limiting effect on the nucleation kinetics of ions and its ability to increase the nucleation barrier of calcium carbonate by altering the normal pathway of calcium carbonate polymorph formation. Further analysis indicates that the ion-limiting effect and the polymorph control ability of GO may stem from its oxygen functional group-rich surface chemistry and two-dimensional (2D) planar features, which endow GO with a Ca2+ binding ability and additional steric hindrance for CO32- diffusion, respectively.

Reverse osmosis membrane functionalized with aminated graphene oxide and polydopamine nanospheres plugging for enhanced NDMA rejection and anti-fouling performance

The use of reverse osmosis (RO) for water reclamation has become an essential part of the water supply owing to the ever-increasing water demand and the utmost performance of the RO membranes. Despite the global RO implementation, its inferior rejection against low molecular weight contaminants of emerging concerns (CECs) (i.e., N-nitrosodimethylamine (NDMA)) and propensity to fouling remain bottle-neck thus affecting process robustness for water reuse. This study aims to enhance both the rejection and antifouling properties of the RO membrane. Herein for the first time, we report RO membrane modification using polydopamine nanospheres (PDAns) followed by aminated-graphene oxide (AGO) deposition as an effective approach to overcome these challenges. The modification of the RO membrane using PDAns-AGO resulted in 89.3 ± 2.7% rejection compared to the pristine RO membrane which demonstrated 69.2 ± 2.1% NDMA rejection. This significant improvement can be ascribed to the plugging and shielding of defective areas (formed during interfacial polymerization) of the polyamide layer through active PDAns and AGO layers and to the added sieving mechanism that arose through narrow channels of the AGO owing to its reduction. Moreover, the in-situ and non-destructive fouling monitoring using optical coherence tomography (OCT) revealed that the PDAns-AGO coating enhanced both the anti-scaling and anti-biofouling characteristics. The improved hydrophilicity and bactericidal effect together with roughness and surface charge suppression synergistically enhanced anti-fouling properties. This study provides a new direction for safe and cost-effective water reuse practices. The membrane with high selectivity against CECs such as NDMA has the potential to eliminate permeate staging using second pass RO and other advanced oxidation processes which are utilized as a tertiary treatment to make reclaimed water suitable for potable/non-potable application.

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.

Calcium Sulfate and Calcium Carbonate Scaling of Thin-Film Composite Polyamide Reverse Osmosis Membranes with Surface-Tethered Polyacrylic Acid Chains

The gypsum and calcite scaling propensities of the thin-film composite polyamide (PA-TFC) reverse osmosis (RO) membrane, modified with a tethered surface layer of polyacrylic acid (PAA) chains, was evaluated and compared to the scaling of selected commercial RO membranes. The tethered PAA layer was synthesized onto a commercial polyamide membrane (i.e., base-PA) via atmospheric pressure plasma-induced graft polymerization (APPIGP). The PAA nano-structured (SNS) base-PA membrane (SNS-PAA-PA) was scaled to a lesser degree, as quantified by a lower permeate flux decline and surface imaging, relative to the tested commercial membranes (Dow SW30, Toray SWRO, and BWRO). The cleaning of gypsum-scaled membranes with D.I. water flushing achieved 100% water permeability recovery for both the SNS-PAA-PA and Dow SW30 membranes, relative to 92-98% permeability restoration for the Toray membranes. The calcium carbonate scaling of SNS-PAA-PA membranes was also lower relative to the commercial membranes, but permeability recovery after D.I. water cleaning was somewhat lower (94%) but consistent with the level of surface scale coverage. In contrast, the calcite and gypsum-scaled membrane areas of the commercial membranes post-cleaning were significantly higher than for the SNS-PAA-PA membrane but with 100% permeability recovery, suggesting the potential for membrane damage when mineral scaling is severe.

Ionic Strength-Dependent Attachment of Pseudomonas aeruginosa PAO1 on Graphene Oxide Surfaces

Graphene oxide (GO) is a widely used antimicrobial and antibiofouling material in surface modification. Although the antibacterial mechanisms of GO have been thoroughly elucidated, the dynamics of bacterial attachment on GO surfaces under environmentally relevant conditions remain largely unknown. In this study, quartz crystal microbalance with dissipation monitoring (QCM-D) was used to examine the dynamic attachment processes of a model organism Pseudomonas aeruginosa PAO1 onto GO surface under different ionic strengths (1-600 mM NaCl). Our results show the highest bacterial attachment at moderate ionic strengths (200-400 mM). The quantitative model of QCM-D reveals that the enhanced bacterial attachment is attributed to the higher contact area between bacterial cells and GO surface. The extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory and atomic force microscopy (AFM) analysis were employed to reveal the mechanisms of the bacteria-GO interactions under different ionic strengths. The strong electrostatic and steric repulsion at low ionic strengths (1-100 mM) was found to hinder the bacteria-GO interaction, while the limited polymer bridging caused by the collapse of biopolymer layers reduced cell attachment at a high ionic strength (600 mM). These findings advance our understanding of the ionic strength-dependent bacteria-GO interaction and provide implications to further improve the antibiofouling performance of GO-modified surfaces.

Recent Advances in Responsive Membrane Functionalization Approaches and Applications

In recent years, significant advances have been made in the field of functionalized membranes. With the functionalization using various materials, such as polymers and enzymes, membranes can exhibit property changes in response to an environmental stimulation, such as heat, light, ionic strength, or pH. The resulting responsive nature allows for an increased breadth of membrane uses, due to the developed functionalization properties, such as smart-gating filtration for size-selective water contaminant removal, self-cleaning antifouling surfaces, increased scalability options, and highly sensitive molecular detection. In this review, new advances in both fabrication and applications of functionalized membranes are reported and summarized, including temperature-responsive, pH-responsive, light-responsive, enzyme-functionalized, and two-dimensional material-functionalized membranes. Specific emphasis was given to the most recent technological improvements, current limitations, advances in characterization techniques, and future directions for the field of functionalized membranes.

Corrosion in seawater desalination industry: A critical analysis of impacts and mitigation strategies

In the current world, freshwater production by clean energy sources with minimum environmental footprints is the main challenge for humankind which is dramatically deteriorating by overexploitation of available water resources. Seawater desalination technology greatly contributes to the mitigation of these serious conditions to produce potable water. However, because desalination plants handle extremely aggressive seawater under stringent operational conditions, they are highly vulnerable to insidious effects of corrosion primarily in the form of general and localized corrosion. Moreover, mineral scaling and bio-fouling are major challenges that further exacerbate corrosion phenomena. So, to ensure the continual operation and curbing corrosion in seawater desalination systems, strict monitoring and selection of highly corrosion-resistance materials are of prime concern. The present paper briefly explores fundamental concepts of corrosion in the desalination industry besides discussing different mitigation strategies for reducing the pernicious effects of corrosion which gravely impair environment quality and durability of desalination infrastructures. Moreover, the authors propose the knowledge gaps and perspectives to delineate the future research direction. Effective solutions for avoiding seawater stagnation, developing highly sophisticated coatings and surface modification technologies, application of advanced computational programs for accurate prediction of possible corrosion failure in desalination plants, and using quantum technology and magnetic corrosion inhibitor in seawater desalination are recommended as an urgent future research focus to combat against corrosion. On the whole, despite outstanding breakthroughs in the field of corrosion control in the desalination industry, the long-term performance of current materials is highly controversial as still many cases of corrosion failures have been reported which indicates the necessity of intensive research work.

Electrocatalytic hydrodechlorination system with antiscaling and anti-chlorine poisoning features for salt-laden wastewater treatment

The high salinity and coexistence of scaling ions (Ca²⁺, Mg²⁺, HCO₃^-) in wastewater challenge the efficacy and durability of palladium (Pd)-mediated electrocatalytic hydrodechlorination (EHDC) reaction for chlorinated organic pollutant detoxification, due to the accompanying Cl^- poisoning at Pd sites and scaling on electrode. In a concentrated NaCl solution (5.8 g L ^- 1) with Ca²⁺ (80.0 mg L ^- 1), Mg²⁺ (30.0 mg L ^- 1) and HCO₃^- (180.0 mg L ^- 1), the EHDC efficiency of Pd towards 2,4-dichlorophenol decreases significantly from 67.8% to 33.1% in 72.0 h of reaction, and the electrode is covered with layers of fluffy aragonite precipitate. Herein we demonstrate the inclusion of a commercial antiscalant 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) can prevent both scale formation and Cl^- poisoning, leading to an efficient and steady EHDC process. A mechanistic study reveals that the unique dual function of PBTC primarily originates from the bearing phosphonate and carboxyl groups. With the large affinity of these groups (especially the phosphonate group) for scaling cations and Pd, the PBTC can chelate and stabilize the scaling cations in water and replace Cl^- at Pd surface. It can also release protons, and trigger the formation of more electron-deficient Pd^δ+ species via PBTC-Pd binding, leading to an enhanced EHDC. This work provides effective solutions to the scaling/poisoning issues that commonly encountered in real wastewater and paves a solid road for EHDC application in pollution abatement.

Optimization of Polyacrylic Acid Coating on Graphene Oxide-Functionalized Reverse-Osmosis Membrane Using UV Radiation through Response Surface Methodology

Reverse osmosis (RO) is affected by multiple types of fouling such as biofouling, scaling, and organic fouling. Therefore, a multi-functional membrane capable of reducing more than one type of fouling is a need of the hour. The polyacrylic acid and graphene oxide (PAA-GO) nanocomposite functionalization of the RO membrane has shown its effectiveness against both mineral scaling and biofouling. In this research, the polyacrylic acid concentration and irradiation times were optimized for the PAA-GO-coated RO membrane using the response surface methodology (RSM) approach. The effect of these parameters on pure water permeability and salt rejection was investigated. The models were developed through the design of the experiment (DoE), which were further validated through the analysis of variance (ANOVA). The optimum conditions were found to be: 11.41 mg·L⁻¹ (acrylic acid concentration) and 28.08 min (UV activation times) with the predicted results of 2.12 LMH·bar⁻¹ and 98.5% NaCl rejection. The optimized membrane was prepared as per the model conditions, which showed an increase in both pure water permeability and salt rejection as compared to the control. The improvement in membrane surface smoothness and hydrophilicity for the optimized membrane also helped to inhibit mineral scaling by 98%.

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.

Liquid-Infused Membranes Exhibit Stable Flux and Fouling Resistance

Antifouling membranes that offer excellent operational lifetimes are critical technologies needed to meet the growing demand for clean water. In this study, we demonstrate antifouling membranes featuring an ultrathin oil layer that stayed immobilized on the surface and in the pore walls of poly(vinylidene fluoride) membranes for multiple cycles of operation at industrially relevant transmembrane pressures. An optimized quantity of a commercial Krytox oil with either a low (K103) or a high viscosity (K107) was infused onto the active surface and into the pores of membranes with a 0.45 μm pore size. The presence of the oil layer was qualitatively confirmed using crystal violet staining and variable pressure scanning electron microscopy. Using a dead-end stirred cell, a consistent pure water permeance value of 3000 L m^-2 h^-1 bar^-1 was achieved for the K103 liquid-infused membranes for at least 10 operation cycles, which was expectedly lower than the permeance of bare control membranes (∼16 000 L m^-2 h^-1 bar^-1), suggesting that a stable oil layer was formed on all membrane-active sites. To quantify if oil was lost during membrane operation, extensive thermogravimetric analysis was conducted on both the as-prepared and used membranes. When challenged with the microorganism, Escherichia coli K12, the liquid-infused membranes statistically reduced microbial attachment by ∼50% versus the control membranes. For the first time, we have demonstrated that by forming an immobilized, robust, and stable oil-coated membrane, we can generate high-performance membranes with stable permeance values that can be operated at relevant transmembrane pressures and provide long-lasting antifouling properties.

Mineral Scaling on Reverse Osmosis Membranes: Role of Mass, Orientation, and Crystallinity on Permeability

Prior mineral scaling investigations mainly studied the effects of membrane surface properties rather than on the mineral properties and their impact on membrane permeability. In our study, mass, crystal growth orientation, and crystallinity of mineral precipitates on membranes, as well as their effects on membrane permeability have been investigated. Gypsum scaling tests on bare and bovine serum albumin (BSA)-conditioned membranes were conducted under different saturation indices. Results show that a longer scaling period was required for BSA-conditioned membranes to reach the same membrane permeate flux decline as bare membranes. Though the final reduced permeability was the same for both two membranes, the masses of the mineral precipitates on BSA-conditioned membranes were around two times more than those on bare membranes. Further mineral characterizations confirmed that different permeability decay rates of both types of the membrane were attributed to the differences in growth orientations rather than amounts of gypsum precipitates. Moreover, BSA-conditioned layers with high carboxylic density and specific molecular structure could stabilize bassanite and disrupt the oriented growth to inhibit the formation of needle-like gypsum crystals as observed on bare membranes, thus resulting in lower surface coverage with scales on membranes and alleviating the detrimental scaling effect on membrane permeability.

Development of Environment-Friendly Membrane for Oily Industrial Wastewater Filtration

Latex phase blending and crosslinking method was used in this research work to produce nitrile butadiene rubber-graphene oxide (NBR-GO) membranes. This fabrication technique is new and yields environmentally friendly membranes for oil-water separation. GO loading was varied from 0.5 to 2.0 part per hundred-part rubber (pphr) to study its effect on the performance of NBR-GO membrane. GO was found to alter the surface morphology of the NBR matrix by introducing creases and fold on its surface, which then increases the permeation flux and rejection rate efficiency of the membrane. X-Ray diffraction analysis proves that GO was well dispersed in the membrane due to the non-existence of GO fingerprint diffraction peak at 2θ value of 10-12° in the membrane samples. The membrane filled with 2.0 pphr GO has the capability to permeate 7688.54 Lm-2 h-1 water at operating pressure of 0.3 bar with the corresponding rejection rate of oil recorded at 94.89%. As the GO loading increases from 0.5 to 2.0 pphr, fouling on the membrane surface also increases from Rt value of 45.03% to 87.96%. However, 100% recovery on membrane performance could be achieved by chemical backwashing.