Advanced Anti-Fouling Membranes for Osmotic Power Generation from Wastewater via Pressure Retarded Osmosis (PRO)

Formation of Zwitterionic and Self-Healable Hydrogels via Amino-yne Click Chemistry for Development of Cellular Scaffold and Tumor Spheroid Phantom for MRI

In situ-forming biocompatible hydrogels have great potential in various medical applications. Here, we introduce a pH-responsive, self-healable, and biocompatible hydrogel for cell scaffolds and the development of a tumor spheroid phantom for magnetic resonance imaging. The hydrogel (pMAD) was synthesized via amino-yne click chemistry between poly(2-methacryloyloxyethyl phosphorylcholine-co-2-aminoethylmethacrylamide) and dialkyne polyethylene glycol. Rheology analysis, compressive mechanical testing, and gravimetric analysis were employed to investigate the gelation time, mechanical properties, equilibrium swelling, and degradability of pMAD hydrogels. The reversible enamine and imine bond mechanisms leading to the sol-to-gel transition in acidic conditions (pH ≤ 5) were observed. The pMAD hydrogel demonstrated potential as a cellular scaffold, exhibiting high viability and NIH-3T3 fibroblast cell encapsulation under mild conditions (37 °C, pH 7.4). Additionally, the pMAD hydrogel also demonstrated the capability for in vitro magnetic resonance imaging of glioblastoma tumor spheroids based on the chemical exchange saturation transfer effect. Given its advantages, the pMAD hydrogel emerges as a promising material for diverse biomedical applications, including cell carriers, bioimaging, and therapeutic agent delivery.

Effects of Carbon Spacer Length on Conformational Transitions and Protein Adsorption of Polyzwitterions

The properties of polyzwitterions are closely linked to their carbon spacer length (CSL) between oppositely charged groups. A thorough understanding of the effect of CSL on the properties of polyzwitterion-functionalized membranes is important for their fouling resistance and separation performances. In this work, polyzwitterion-functionalized membranes with different CSLs are prepared by coupling selective swelling-induced pore generation with zwitterionization, and the investigation is focused on comprehending the molecular mechanisms underlying protein resistance and conformational transitions within polyzwitterions under varying CSLs. The zwitterionized films show an enhancement in the surface negative potential with the increase of CSL, attributed to the negatively charged groups distanced from the positively charged groups. Quartz crystal microbalance with dissipation (QCM-D) demonstrates that zwitterionized films with different CSLs display distinct levels of resistance to protein adsorption. The trimethylamine N-oxide-derived polymer (PTMAO, CSL = 0) zwitterionized film shows the highest resistance compared to the poly(3-[dimethyl(2'-methacryloyloxyethyl] ammonio) ethanesulfonate (PMAES, CSL = 2) zwitterionized film and the poly(sulfobetaine methacrylate) (PSBMA, CSL = 3) zwitterionized film, owing to its electrical neutrality and pronounced hydrophilicity. Moreover, analysis of the anti-polyelectrolyte behaviors reveals that PTMAO does not undergo a significant conformation transition in deionized water and salt solutions, while the conformations of PMAES and PSBMA display to be more salt-dependent as the CSL increases, attributed to their increased polarization and dipole moment. As a result, the permeability of zwitterionized membranes exhibits enhanced salt responsiveness with the increase in CSL. The findings of this study are expected to facilitate the design of adsorption-resistant surfaces desired in diverse fields.

Bacterial nanocellulose membrane with opposite surface charges for large-scale and large-area osmotic energy harvesting and ion transport

How to optimize ion-exchange membrane materials has been the key for researchers recently working on the use of reverse electrodialysis to harvest osmotic energy. Based on the considerations of improving membrane performance and conversion to large-area industrial production, this work first proposes an easy-industrialized strategy to treat bacterial cellulose membranes by hot pressing and hot pressing with etherification modification, and then to obtain anion-selective and cation-selective membrane pairs (PBC-M and NBC-M) with opposite charges. The PBC-M obtained by multi-step treatment has excellent hydrophobicity, good surface charge density, and more favorable nanochannel size for the functioning of double layer. The maximum output power density of 44.1 mW m-2 was obtained in artificial river water and seawater simulated salinity gradient power generation. Applied to a larger test area, the power output of the system where a single membrane is located can reach 2.2 × 10-3 mW, which is ahead of similar experimental products. The two membranes prepared can also be used in combination, which provides a new idea for full cell design. It's important to open up a new route for optimizing nanofluidic channel design, regulating ion flux transport, and advancing the large-scale industrialization of biomass nanofluidic membrane RED system.

Adsorption Dynamics of Uremic Toxins to Novel Modified Magnetic Nanoparticles

Kidney dysfunction leads to the retention of metabolites in the blood compartment, some of which reach toxic levels. Uremic toxins are associated with the progression of kidney disease and other symptoms of kidney failure (i.e., nausea, itchiness, and hypertension). Toxin removal ameliorates symptoms and reduces further organ damage, but membrane-based methods are inadequate for this purpose. Engineered adsorbents may facilitate enhanced removal of retained toxins, especially those bound strongly by proteins. Poly 2-(methacryloyloxy)ethyl phosphorylcholine-co-β-cyclodextrin (p(MPC-co-PMβCD)) coated magnetic nanoparticles are synthesized, characterized for their physicochemical properties (Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), thermogravimetric analysis(TGA), gel permeation chromatography (GPC), and transmission electron microscope (TEM), and evaluated toxin adsorption from a complex solution for the first time to quantify the effects of film chemistry and incubation time on the adsorbed toxinome (the collection of toxins). Uremic toxins are bound by even "low-fouling" polymer films themselves; providing further insight into how small molecule interactions with "low-fouling" films may affect protein-surface interactions. These results suggest a dynamic interaction between toxins and surfaces that is not driven by solution concentration alone. This knowledge will help advance the design of novel adsorbent films for clearing uremic toxins.

Engineering Radioactive Microspheres for Intra‐Arterial Brachytherapy Using Radiation‐Induced Graft Polymerization

Intravascular brachytherapy requires advances in radio‐embolization technologies that combine brilliant radiostability efficacy with a facile and green synthesis route. A hybrid‐integrated radioactive microsphere strategy using phosphorylcholine‐modified lutetium‐177 coordinated polymeric microspheres (177Lu‐PCMs) is reported that are fabricated via radiation‐induced graft polymerization for imaging‐guided locoregional intravascular brachytherapy. The underlying formation mechanism of 177Lu‐PCMs is elucidated using first‐principles computations and density functional theory calculations, and 177Lu loading mechanisms are investigated with Near‐edge and extended X‐ray absorption fine structure spectroscopy. The engineered 177Lu‐PCMs exhibit excellent mechanical properties, good hydrophilicity, and controlled sphere diameter. These features provide advantages of ultra‐stable embolic radio‐theranostics, which is demonstrated in different preclinical rodent models and isolated human liver tumor tissues. During locoregional intra‐arterial brachytherapy, 177Lu‐PCMs can be visualized via SPECT to validate the in vivo biodistribution and retention in real time, achieving precise delivery, effective anti‐cancer treatment, and a distinguished safety profile without degradation, ectopic embolization, and adverse reactions. Therefore, this study offer a new avenue for the development of a highly innovative and translational approach for precision intra‐arterial brachytherapy.

Harvesting Blue Energy Based on Salinity and Temperature Gradient: Challenges, Solutions, and Opportunities

Greenhouse gas emissions associated with power generation from fossil fuel combustion account for 25% of global emissions and, thus, contribute greatly to climate change. Renewable energy sources, like wind and solar, have reached a mature stage, with costs aligning with those of fossil fuel-derived power but suffer from the challenge of intermittency due to the variability of wind and sunlight. This study aims to explore the viability of salinity gradient power, or "blue energy", as a clean, renewable source of uninterrupted, base-load power generation. Harnessing the salinity gradient energy from river estuaries worldwide could meet a substantial portion of the global electricity demand (approximately 7%). Pressure retarded osmosis (PRO) and reverse electrodialysis (RED) are more prominent technologies for blue energy harvesting, whereas thermo-osmotic energy conversion (TOEC) is emerging with new promise. This review scrutinizes the obstacles encountered in developing osmotic power generation using membrane-based methods and presents potential solutions to overcome challenges in practical applications. While certain strategies have shown promise in addressing some of these obstacles, further research is still required to enhance the energy efficiency and feasibility of membrane-based processes, enabling their large-scale implementation in osmotic energy harvesting.

Forward osmosis membrane doped with water-based zirconium fumarate MOFs to enhance dye pollutant removal and membrane antifouling performance

Metal-organic frameworks (MOFs) can be applied to enhance the property of forward osmosis membranes. However, organic solvents can easily remain in organic synthetic metal-organic frame materials and cause membrane fouling and a decrease in membrane permeability. In this study, water-based Zr-fumarate MOFs were synthesized and doped into the membrane active layer by interfacial polymerization to provide a water-based MOF-doped thin-film composite membrane (TFC membrane). It was found that doping the water-based MOFs effectively improved membrane hydrophilicity, and nanowater passages were introduced in the active layer to improve permeability. The water flux of the water-based MOF-doped TFC membranes was increased by 21% over that of the original membrane, and the selectivity performance of the membrane was improved while keeping the salt rejection basically unchanged. Additionally, the water-based MOF-doped TFC membrane showed good removal efficiency (R_d > 94%) and strong antipollution performance in the treatment of dye pollutants.

In Situ Chemical Modification with Zwitterionic Copolymers of Nanofiltration Membranes: Cure for the Trade-Off between Filtration and Antifouling Performance

Breaking the trade-off between filtration performance and antifouling property is critical to enabling a thin-film nanocomposite (TFC) nanofiltration (NF) membrane for a wide range of feed streams. We proposed a novel design route for TFC NF membranes by grafting well-defined zwitterionic copolymers of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA) and 2-aminoethyl methacrylate hydrochloride (AEMA) on the polyamide surfaces via an in situ surface chemical modification process. The successful grafting of a zwitterionic copolymer imparted the modified NF membranes with better surface hydrophilicity, a larger actual surface area (i.e., nodular structures), and a thinner polyamide layer. As a result, the water permeability of the modified membrane (i.e., TFC-10) was triple that of the pristine TFC membrane while maintaining high Na₂SO₄ rejection. We further demonstrated that the TFC-10 membrane possessed exceptional antifouling properties in both static adsorption tests and three cycles of dynamic protein and humic acid fouling tests. To recap, this work provides valuable insights and strategies for the fabrication of TFC NF membranes with simultaneously enhanced filtration performance and antifouling property.

Electrospraying Zwitterionic Copolymers as an Effective Biofouling Control for Accurate and Continuous Monitoring of Wastewater Dynamics in a Real-Time and Long-Term Manner

Long-term continuous monitoring (LTCM) of water quality can provide high-fidelity datasets essential for executing swift control and enhancing system efficiency. One roadblock for LTCM using solid-state ion-selective electrode (S-ISE) sensors is biofouling on the sensor surface, which perturbs analyte mass transfer and deteriorates the sensor reading accuracy. This study advanced the anti-biofouling property of S-ISE sensors through precisely coating a self-assembled channel-type zwitterionic copolymer poly(trifluoroethyl methacrylate-random-sulfobetaine methacrylate) (PTFEMA-r-SBMA) on the sensor surface using electrospray. The PTFEMA-r-SBMA membrane exhibits exceptional permeability and selectivity to primary ions in water solutions. NH₄⁺ S-ISE sensors with this anti-fouling zwitterionic layer were examined in real wastewater for 55 days consecutively, exhibiting sensitivity close to the theoretical value (59.18 mV/dec) and long-term stability (error <4 mg/L). Furthermore, a denoising data processing algorithm (DDPA) was developed to further improve the sensor accuracy, reducing the S-ISE sensor error to only 1.2 mg/L after 50 days of real wastewater analysis. Based on the dynamic energy cost function and carbon footprint models, LTCM is expected to save 44.9% NH₄⁺ discharge, 12.8% energy consumption, and 26.7% greenhouse emission under normal operational conditions. This study unveils an innovative LTCM methodology by integrating advanced materials (anti-fouling layer coating) with sensor data processing (DDPA).

Adhesion force evolution of protein on the surfaces with varied hydration extent: Quantitative determination via atomic force microscopy

The adhesion force evolution of protein on surfaces with continuously varied hydrophobicity/hydration layer has not been completely clarified yet, limiting the further development of environmental applications such as membrane anti-biofouling and selective adsorption of the functional surfaces. Herein, chemical force spectroscopy using atomic force microscopy (AFM) was utilized to quantify the evolution of the adhesion forces of protein on hydration surfaces in water, where bovine serum albumin (BSA) was immobilized on an AFM tip as the representative protein. The stiffness, roughness and charge properties of the substrate surfaces were kept constant and the hydrophobicity was the only variant to monitor the role of hydrated water layers in protein adhesion. The adhesion force increased non-monotonically as a function of hydrophobicity of substrate surfaces, which was related to the concentration of humic acid, and independent of pH values and ionic strength. The non-monotonic variation occurred in the range of contact angle at 60-80° due to the mutual restriction between solid-liquid interface energy and solid-solid interface energy. Hydrophobic attraction was the dominant force that drove adhesion of BSA to these model substrate surfaces, but the passivation of hydration layers at the interface could weaken the hydrophobic attraction. In contrast to the measurements in water, the adhesion forces decreased as a function of surface hydrophobicity when measured in air, because capillary forces from condensation water dominated adhesion forces. The passivation of hydration layers of protein was revealed by quantitatively determining the evolution of adhesion forces on the hydration surfaces of varying hydrophobicity, which was ignored by traditional adhesion theory.

Miniaturized Salinity Gradient Energy Harvesting Devices

Harvesting salinity gradient energy, also known as "osmotic energy" or "blue energy", generated from the free energy mixing of seawater and fresh river water provides a renewable and sustainable alternative for circumventing the recent upsurge in global energy consumption. The osmotic pressure resulting from mixing water streams with different salinities can be converted into electrical energy driven by a potential difference or ionic gradients. Reversed-electrodialysis (RED) has become more prominent among the conventional membrane-based separation methodologies due to its higher energy efficiency and lesser susceptibility to membrane fouling than pressure-retarded osmosis (PRO). However, the ion-exchange membranes used for RED systems often encounter limitations while adapting to a real-world system due to their limited pore sizes and internal resistance. The worldwide demand for clean energy production has reinvigorated the interest in salinity gradient energy conversion. In addition to the large energy conversion devices, the miniaturized devices used for powering a portable or wearable micro-device have attracted much attention. This review provides insights into developing miniaturized salinity gradient energy harvesting devices and recent advances in the membranes designed for optimized osmotic power extraction. Furthermore, we present various applications utilizing the salinity gradient energy conversion.

Zwitterionic Copolymer-Regulated Interfacial Polymerization for Highly Permselective Nanofiltration Membrane

A highly permselective nanofiltration membrane was engineered via zwitterionic copolymer assembly regulated interfacial polymerization (IP). The copolymer was molecularly synthesized using single-step free-radical polymerization between 2-methacryloyloxyethyl phosphorylcholine (MPC) and 2-aminoethyl methacrylate hydrochloride (AEMA) (P[MPC-co-AEMA]). The dynamic network of P[MPC-co-AEMA] served as a regulator to precisely control the kinetics of the reaction by decelerating the transport of piperazine toward the water/hexane interface, forming a polyamide (PA) membrane with ultralow thickness of 70 nm, compared to that of the pristine PA (230 nm). Concomitantly, manipulating the phosphate moieties of P[MPC-co-AEMA] integrated into the PA matrix enabled the formation of ridge-shaped nanofilms with loose internal architecture exhibiting enhanced inner-pore interconnectivity. The resultant P[MPC-co-AEMA]-incorporated PA membrane exhibited a high water permeance of 15.7 L·m^-2·h^-1·bar^-1 (more than 3-fold higher than that of the pristine PA [4.4 L·m^-2·h^-1·bar^-1]), high divalent salt rejection of 98.3%, and competitive mono-/divalent ion selectivity of 52.9 among the state-of-the-art desalination membranes.

Recent development of pressure retarded osmosis membranes for water and energy sustainability: A critical review

With the goal of zero-liquid discharge and green energy harvest, extraction of abundant green energy from saline water via pressure retarded osmosis (PRO) technology is a promising but challenging issue for water treatment technologies to achieve water and energy sustainability. Development of high performance PRO membranes has received increased concerns yet still under controversy in practical applications. In this review, a comprehensive and up-to-date discussion of some key historical developments is first introduced covering the major advances of PRO engineering applications and novel membranes especially made in recent years. Then the critical performance indicators of PRO membranes including water flux and power density are briefly discussed. Subsequently, sufficient discussion on four performance limiting factors in PRO membrane and process is presented including concentration polarization, reverse solute diffusion, membrane fouling and mechanical stability. To fully address these issues, an updated insight is provided into recent major progresses on advanced fabrication and modification techniques of novel PRO membranes featuring enhanced performance with different configurations and materials, which are also reviewed in detail based on the viewpoint of design rationales. Afterwards, antifouling strategies and engineering applications are critically introduced. Finally, conclusions and future perspective of PRO membrane for practical operation are briefly discussed.

Influence of hydrodynamic operating conditions on organic fouling of spiral-wound forward osmosis membranes: Fouling-induced performance deterioration in FO-RO hybrid system

The forward osmosis-reverse osmosis (FO-RO) hybrid process has been extensively researched as part of attempts to reduce the high energy consumption of conventional seawater reverse osmosis in recent years. FO operating conditions play a substantial role in the hybrid process, dictating not only the performance of the entire system but also the propensity for fouling, which deteriorates performance in long-term field operations. Therefore, determining the optimal FO operating conditions with regard to membrane fouling may promote sustainable operation through efficient fouling control. This study thus evaluated the influence of each hydrodynamic operating condition (feed flowrate, draw flowrate, and hydraulic pressure difference) and their synergistic effects on fouling propensity in a pilot-scale FO operation under seawater and municipal wastewater conditions. Fouling-induced variation in water flux, channel pressure drop, diluted concentration, and the resulting specific energy consumption (SEC) were comparatively analyzed and utilized to project performance variation in a full-scale FO-RO system. Fouling-induced performance reduction significantly varied depending on hydrodynamic operating conditions and the resultant fouling propensity during 15 days of continuous operation. A high feed flowrate demonstrated a clear ability to mitigate fouling-induced performance deterioration in all conditions. A high draw flowrate turned out to be detrimental for fouling propensity since its high reverse solute flux accelerated fouling growth. Applying additional hydraulic pressure during FO operation caused a faster reduction of water flux, and thus feed recovery and water production; however, these drawbacks could be compensated for by a 10% reduction in the required FO membrane area and an additional reduction in RO SEC.

Membrane processes

This literature review provides a review for publications in 2018 and 2019 and includes information membrane processes findings for municipal and industrial applications. This review is a subsection of the annual Water Environment Federation literature review for Treatment Systems section. The following topics are covered in this literature review: industrial wastewater and membrane. Bioreactor (MBR) configuration, membrane fouling, design, reuse, nutrient removal, operation, anaerobic membrane systems, microconstituents removal, membrane technology advances, and modeling. Other sub-sections of the Treatment Systems section that might relate to this literature review include the following: Biological Fixed-Film Systems, Activated Sludge, and Other Aerobic Suspended Culture Processes, Anaerobic Processes, and Water Reclamation and Reuse. This publication might also have related information on membrane processes: Industrial Wastes, Hazardous Wastes, and Fate and Effects of Pollutants.

Pressure retarded osmosis coupled with activated sludge process for wastewater treatment: Performance and fouling behaviors

A novel hybrid technology integrating pressure retarded osmosis with activated sludge process (denoted as PRO-MBR) was proposed in this study for wastewater treatment. Here, performance and fouling behaviors of PRO-MBR were investigated. Excellent contaminants removal and power production were simultaneously achieved in the PRO-MBR. A significant drop of water flux in the PRO-MBR was mainly due to the severe fouling of the support layer in forward osmosis (FO) membrane including internal fouling and external fouling. Although the external fouling was identified to be the major type of fouling, the internal fouling dominated the overall decline of water flux. In addition, organic foulants and biofoulants were the dominant foulants for the external fouling while inorganic foulants were equal to organic foulants and biofoulants for the internal fouling. According to the variations of water flux in the PRO-MBR, the development of support layer fouling was divided into three stages.

Zwitterion-Ag Complexes That Simultaneously Enhance Biofouling Resistance and Silver Binding Capability of Thin Film Composite Membranes

Biofouling can be overcome with zwitterion grafts and antimicrobial, metallic nanoparticles. However, the mechanism underpinning this effective approach remains unclear. To elucidate the role of each component in this system while maximizing membrane antifouling and antimicrobial properties, here we performed a comparative study to investigate the impact of zwitterion type and their interactions with Ag of various states. Two different zwitterions (SO₃^--based and COO^--based) were employed to modify polyamide (PA) thin film composite (TFC) membranes, and the metallized and mineralized membranes were developed via in situ formation of silver (Ag) nanoparticles and deposition of silver chloride (AgCl) particles on the zwitterion-modified TFC membranes. The presence of zwitterions was key to enhance Ag content, resulting in significantly improved antimicrobial and antifouling properties without compromising the nanofiltration separation performance. COO^--based zwitterions were found more favorable toward Ag metallization and mineralization compared to SO₃^--based zwitterions. The underlying mechanisms underpinning this discovery were further revealed using density functional theory (DFT) to reveal Gibbs free energy of the binding between zwitterions and Ag⁺ ions. This fundamental knowledge is crucial for designing next-generation antibiofouling strategies.

Understanding the Antifouling Mechanism of Zwitterionic Monomer-Grafted Polyvinylidene Difluoride Membranes: A Comparative Experimental and Molecular Dynamics Simulation Study

The antifouling process of the membrane is very vital for the highly efficient treatment of industrial wastewater, especially high salinity wastewater containing oil and other pollutants. In the present work, the dynamical antifouling mechanism is explored via molecular dynamics simulations, while the corresponding experiments about surface properties of the zwitterionic monomer-grafted polyvinylidene difluoride membrane are designed to verify the simulated mechanism. Water can form a stable hydration layer at the grafted membrane surface, where all the simulated radial distribution function of water/membrane, hydrogen bond number, water diffusivity, and experimental oil contact angles are stable. However, the water flux across the membrane will increase first and then decrease as the grafting ratio increases, which not only depends on the reduced pore size of the zwitterionic monomer-grafted membrane but also results from water diffusion. Furthermore, the dynamical fouling processes of pollutants (taking sodium alginate as an example) on the grafted membrane in water and brine solution are investigated, where both the high grafting ratio and electrolyte CaCl₂ can enhance the fouling energy barrier of the pollutant. The results show that both the enhanced hydrophilic property and the electrostatic repulsion can affect the antifouling capability of the grafted membrane. Finally, the ternary synergistic antifouling mechanisms among the zwitterionic membrane, electrolyte, and pollutant sodium alginates are discussed, which could be helpful for the rational design and preparation of new and highly efficient zwitterionic antifouling membranes.