Improved Water Permeability Research Articles

Experimental Investigation on Pervious Recycled Aggregate Concrete Made of Waste Porcelain

The current study examines the physical, mechanical, and durability of eco-efficient pervious concrete produced with partial and complete substitutions of natural aggregate (NA) by recycled aggregate (RA) waste from demolished concrete and porcelain. The experimental investigation assessed the workability (slump test), compressive strength, flexural strength, and tensile strength along with the concrete's water permeability, impact, and abrasion resistance. Seven mixes were examined; the first is a control mix with natural aggregate, and the other six are made with various RA ratios, including 30%, 70%, and 100%. The sand was also fully replaced by waste porcelain, even though the ratio of sand used in pervious concrete was low. The results revealed that using waste concrete and porcelain adversely affected the workability of fresh pervious concrete mixes, reducing it by approximately 14%. Furthermore, a decrease in the strength of pervious concrete was noticed, especially in the splitting tensile strength, where the reduction reached 32%. Moreover, the impact resistance of pervious concrete made with RA reduced by 29% compared to that made with NA; the same applies to durability, with an increase of 20% in weight loss. On the other hand, using both recycled concrete and recycled porcelain improved the permeability of the pervious concrete, which reached 30%. Pervious concrete made with waste concrete and porcelain can be an acceptable alternative to that made from natural aggregate due to its improved water permeability and positive environmental impact. However, further investigation is important to consider strength and durability enhancement. Doi: 10.28991/CEJ-2024-010-09-08 Full Text: PDF

Utilization of MOF‐enhanced hydrophilic nanocomposite reverse osmosis membrane for desalination with antifouling capabilities

AbstractCellulose acetate (CA) membranes used in reverse osmosis (RO) desalination techniques often face fouling challenges. In this experimental study, the phase inversion method was employed to investigate the incorporation of graphene oxide nanoparticles (GONP) metal–organic frameworks (MOF), into the casting solution for composite CA‐RO membranes. The effects of varying GONP concentrations on fouling resistance and hydrophilicity were evaluated using scanning electron microscopy (SEM), contact angle measurements, and water content analysis. The results demonstrated that the modified CA membrane with 0.05 wt% GONP exhibited improved water permeability (10.3 L/m2 h) and salt rejection (95.8%) compared with the pristine CA membrane. These improvements stem from increased hydrophilicity and reduced fouling. This study's findings suggest that incorporating GONP into the polymeric doped solution can effectively mitigate fouling issues and enhance the performance of RO membranes in desalination applications.Highlights GONP enhances hydrophilicity, reducing fouling in desalination. Effects of varying GONP concentrations were studied. GONP‐CA membrane shows better permeability and salt rejection than pristine. Nanocomposite membranes promise in overcoming fouling in RO membranes.

Research on the application of hydrophilic modified covalent organic framework membranes in seawater desalination

Given the global challenge of freshwater scarcity, the importance of seawater desalination technology has grown. This study examines the efficiency and role of hydrophilic-modified covalent organic framework (COF) membranes in seawater desalination through molecular simulations. Incorporating hydrophilic groups like -SO3H into N2COF membranes and optimizing their structure significantly improved water permeability and salt ion retention. Non-equilibrium molecular dynamics (NEMD) simulations showed that hydrophilic modifications enhance water permeability while preserving salt ion interception efficacy. Furthermore, adjusting the membrane's stacking method could further enhance its seawater desalination performance. The simulations confirm the high-efficiency desalination capability of hydrophilic-modified COF membranes and offer crucial theoretical guidance for designing and preparing high-performance desalination materials.

Novel membrane modifications for pressure retarded osmosis as a new way for sustainable power generation from salinity gradients

Pressure retarded osmosis (PRO) is a novel technology that allows power to be generated from high-salinity resources. To achieve a high power density, a high-salinity solution should be used on the draw side together with high hydraulic pressure, thus the PRO process requires a membrane that has high salt rejection and high pressure resistance. The reverse osmosis (RO) membranes can be potential candidates for the PRO process. In this study, commercial RO membranes with different surface modifications were examined: O2 plasma, polydopamine (PDA) and tannic acid (TA). Improved water permeability and salt rejection were obtained after modification. The membranes were also tested with a high salinity solution (175 g/L NaCl) in a PRO mode. Due to the improved water permeability and high salt rejection of the surface-modified membrane, the commercial RO membrane showed enhanced power density (3 W/m2) in comparison to the pristine membrane (2 W/m2).

GO and surfactant assisted regulation of polyamide nanofiltration membranes for improved separation performance

Fabricating nanofiltration membranes with high water permeance and selectivity by tailoring the structure and morphology is crucial to efficient water purification. In this work, the fabrication of thin film nanocomposite (TFN) nanofiltration membranes by combining two methods, the surfactant-assembly interfacial polymerization (SARIP) and the addition of graphene oxide (GO) or ionic liquid functionalized graphene oxide (GO-IL) for the preparation of the selective PA layer on a novel porous substrate is reported. For the preparation of the porous substrate, mechanically robust, aromatic polyethers containing polar pyridine units (PDSPP) were chosen targeting to improved hydrophilicity and thus enhanced water permeability. The anionic sodium dodecyl sulfate (SDS) surfactant was used to regulate the interfacial polymerization thereby enabling the formation of dense PA layers with high cross-linking degree and consequently high salt rejections. On the other hand, the addition of GO/GO-IL nanosheets could impart hydrophilicity and antifouling properties. The novel porous PDSPP substrate was selected for the fabrication of TFN membranes due to its improved water permeability and superior salt rejection and increased hydrophilicity compared to commercial PSf substrate. The detailed study of the fabricated TFN membranes by ATR-FT-IR, SEM, AFM, XPS, contact angle measurements revealed the formation of polyamide selective layers with rougher surfaces, increased hydrophilicity and high cross-linking degrees (from 44 % to 94 %), resulted from the synergistic effect of SDS and GO incorporation. Moreover, the prepared TFN membranes exhibited high salt rejections while maintaining a moderate water permeability. In particular, the membrane containing the neat GO (TFNGO50) displayed excellent Na2SO4 and MgSO4 rejections (98.8 % and 99.5 %, respectively) while the NaCl rejection was 47.0 % and a water permeability value of 4.2 L m-2h−1 bar−1. The divalent salt rejections were among the highest values reported in the literature in comparison with commercial NF membranes and TFN membranes containing GO/functionalized GO. When GO-IL nanosheets were embedded in the PA layer, the water permeability was slightly improved while the salt rejections were significantly reduced compared to TFNGO50. Lastly, the incorporation of GO enhanced the anti-fouling properties of the prepared membranes due to increased hydrophilicity of the PA surface.

Surface functionalization of polytetrafluoroethylene membrane by polydopamine and quaternary ammonium compound for fouling mitigation in membrane distillation of secondary effluent

Considering the worldwide water scarcity issue, membrane distillation (MD) offers a promising solution for producing reclaimed water from secondary effluent generated by municipal wastewater treatment plants. However, prolonged operation of MD systems can result in membrane fouling, which impairs separation efficiency and shortens the membrane's lifespan. To overcome these challenges, novel surface-modified polytetrafluoroethylene (PTFE) membranes have been developed through a combination of polydopamine deposition and quaternary ammonium compound (QAC) grafting (named as PDQ membranes). The objectives of this preparation are to reduce the membrane hydrophobicity, impart anti-adhesive and bactericidal properties, and improve water permeability and antifouling performance in the MD system. In particular, the membrane coated by a QAC solution with the concentration of 40 mM (named as M3 membrane), achieved a flux of 47.0 LMH, surpassing the original PTFE membrane by 11.4%. During the long-term direct contact membrane distillation operation with the secondary effluent, the M3 membrane exhibited significantly superior antifouling capability than the PTFE membrane. Undergoing three runs of the MD process, the flux reduction of M3 was only 38.1%, whereas the flux of original PTFE membrane experienced a 71.4% decline. The PDQ membranes were also capable of providing stable distillate quality (over 40 h). Notably, the M3 demonstrated a high rejection capability, with an impressive removal efficiency of 96.9% for low molecular weight organics and 92.5% for humus-like substances. Additionally, the PDQ membrane exhibited good anti-bioadhesion and bactericidal properties. This study highlights the promising application potential of the PDQ membrane for fouling mitigation in water and wastewater treatment.

Intercalation of small molecules in the selective layer of polyamide nanofiltration membranes facilitates the separation of Mg2+/Li+

In addressing lithium supply shortages driven by increased energy demand, nanofiltration membrane technology is crucial for recovering lithium from salt lake brines. Overcoming the challenge of achieving high selectivity for Li+ and water permeability in polymer nanofiltration membranes, this study proposes a simple approach using Aminomalononitrile (AMN) intercalation to modify polyamide layers. Density functional theory simulations predict AMN's superior selectivity and enhanced hydrophilicity. Stable intercalation of AMN between polyethyleneimine (PEI) molecules is demonstrated, synergistically enhancing water permeability and Li+ selectivity. The resulting PEI/AMN-TMC membrane exhibits exceptional Li+ selectivity and improved water permeability (13.1 L·m−2·h−1·bar−1), 2.9 times higher than traditional PEI-TMC membranes. Stable performance for over seven days, along with anti-scaling and anti-bacterial properties, underscores its practicality. This investigation sheds light on membrane structure regulation through small-molecule intercalation, offering insights into precise adjustments for enhanced water permeability and ion selectivity.

Organic sandwich-structured carbon fiber/SiO2/PES electrochemical membrane with significantly improved charge transfer efficiency and water permeability

Electrochemical membrane separation has the potential for good degradation efficiency and mitigates membrane fouling. However, it is still a real challenge to further build stable organic substrate and improve its charge efficiency. In this study, an electric conductive and sandwich-structured carbon fiber/SiO2/polyether sulfone (CF/SiO2/PES) membrane showing good tetracycline (TC) removal at both acidic (pH = 3) and alkaline (pH = 9) conditions was fabricated by a facile phase conversion method. The CF/SiO2/PES membrane exhibited notably improved water permeability, augmented by 42 % higher with external voltage than that of the membrane without voltage assistance. Furthermore, the CF/SiO2/PES membrane performance in TC removal was systematically assessed under diverse conditions, encompassing TC concentration, pH values, and applied voltage. The membrane displayed a good removal efficiency of 93.6 % and 91.8 % for TC at acidic and alkaline conditions, respectively. Additionally, the degradation pathway of TC was proposed. Crucially, the CF/SiO2/PES membrane exhibited exceptional reusability and stability over eight consecutive runs. Mechanism study proved that the reactive species play a key role in the TC degradation during electro-filtration. The exceptional permeability, removal efficiency, and recyclability position the CF/SiO2/PES membrane as a promising solution for antibiotic wastewater treatment.

Molecular insight into the separation mechanism of crown Ether-Based channels for lithium Extraction

The shortage of lithium resources can be effectively improved by using membrane separation technology to extract lithium from salt lake brines that contain rich Li. In this study, GO modified with functionalized crown ether group (2)-hydroxymethyl-15-crown-5,15C) was used as a separation membrane for Li+/Mg2+. The effect of 15C and its content on the separation mechanism of Li+/Mg2+ in membrane was designed and studied by molecular dynamics simulation. Improving water permeability of the membrane can be achieved with the appropriate amount of 15Cs, but an excessive amount of 15C will result in channel obstruction, which is not conducive to the transport of water molecules. In addition, the special recognition of Li+ by 15Cs enhances the transmission of Li+ within the channel. Finally, it is found that the dehydration behavior of Li+ is facilitated by the interaction between 15Cs and Li+. As the diameter of Li+ is smaller than the diameter of the 15C cavity, dehydrated Li+ passes through the 15C cavity with ease under pressure. This means that during the separation process, Li+ enters a “dual transport” mode. The membrane gains higher permeability for Li+ while blocking Mg2+. This study clarifies the rapid transport mechanism of Li+ in GO-15C，which provides a feasible strategy for designing highly selective Li+/Mg2+ separation membranes.

Investigations on a solar humidification dehumidification desalination system equipped with various packing materials and multi-stage bubble column dehumidifier.

This work presents the theoretical and experimental investigation of a solar-powered humidification dehumidification desalination (HDD) system with different humidifier packing materials and a two-stage bubble column dehumidifier (BCD). Naturally available coconut shells (CS) and coconut shells with drilled holes (CSH) on the surface to improve water permeability were used as packing materials in the humidifier, and their performance was compared with that of commercial-type pall ring (PR) and raschig ring (RR) packings. An in-house developed numerical model of the HDD system in conjunction with a flat plate solar water collector was used in this study. Steady-state experimental results showed that CSH packing exhibited the highest volumetric mass transfer coefficient (0.00852kg/s), resulting in maximum humidifier efficiency (96%) and freshwater yield (2.16kg/hr), followed by PR (0.00841kg/s, 94%, and 2.137kg/hr), CS (0.00831kg/s, 90%, and 2.127kg/hr), and RR (0.0081kg/s, 81%, and 2.087kg/hr) at feedwater mass flow rate of 1.5kg/min and humidifier inlet temperature of 75 [Formula: see text]. Furthermore, transient outdoor test results showed that using a two-stage configuration in a BCD increased the daily average effectiveness to 0.93, as against 0.79 for a single-stage BCD. Employing CSH instead of PR and RR packings in the humidifier reduced freshwater costs by 6.2% and 7.6%, respectively.

Antifouling and antibacterial bioactive metabolites of marine fungus (terrein)/polyamide thin-film composite reverse osmosis membranes for desalination applications

Marine fungi-derived (+)-terrein is grafted onto a reverse osmosis polyamide membrane using glutaraldehyde, forming a thin film composite (Terrein-PA) membrane. This membrane exhibits improved water permeability, antifouling and antibacterial properties. Compared to conventional reverse osmosis membranes, Terrein-PA membrane shows a 51.0 % increase in permeability (7.4 L/m2·h·bar) due to its beneficial hydroxyl groups. It also effectively inhibits the growth of gram-positive and gram-negative bacteria, achieving antibacterial rates of 98.0 % and 94.9 %, respectively. This reduces microorganism adhesion, extending the membrane's service life. The use of natural (+)-terrein is safer for human health than chlorine treatments. Furthermore, when contaminated with bovine serum albumin, Terrein-PA membrane achieves a flux recovery rate of 90.9 % and a total contamination rate of 12.3 %. This study introduces an innovative approach to produce secure antibacterial reverse osmosis membranes with prolonged lifespan.

Zwitterionic cyclodextrin membrane with uniform subnanometre pores for high-efficient heavy metal ions removal

Polymer nanofiltration (NF) membranes have been widely applied in the desalination, resource substances purification and separation, and wastewater treatment. Nevertheless, direct construction of subnanometre channel polymer membranes for achieving high-efficient metal ions separation is still challenging because of the complicated membrane preparation and difficultly manipulating the membrane pore-size in sub-nanometer. Herein, we exploited a novel subnanometre channel membrane with zwitterionic β-cyclodextrins (ZCDs) by interfacial polymerization. Wherein ZCDs act as building blocks with hydrophobic inner subnanometre cavities and hydrophilic outer rims, allowing for simultaneously improved water permeability and metal ions selectivity. By modulating the zwitterionic monomer grafting ratio of ZCDs and their loading content in the membrane, the ZCDM membrane exhibits high water permeance (J = 21.7 L m−2 h−1∙bar−1) and heavy metal ions rejection, e.g., RCr3+ = 99.8%, RFe3+ = 98.9%, respectively, these values outperform the state-of-the-art NF membranes. Moreover, the ZCDM membrane has good stability and anti-fouling/-bacterial properties, e.g., the water flux recovery ratio and anti-bacterial ratio is >97% and >99%, in the long-term running process. This work offers a feasible strategy for constructing polymer membranes with uniform subnanometre pore, and demonstrates their potential for the heavy metal separation and wastewater treatment.

Overcoming the trade-off between water flux and salt rejection of an RO membrane via simultaneous optimization using highly porous microstructured support and sulfonated porous organic polymer-based polyamide active layer

Many researchers have devoted much effort to addressing the trade-off between water flux and salt rejection of reverse osmosis (RO) membranes till now, but it still needs to be solved. In this work, as a strategy to overcome the trade-off, simultaneous optimization was carried out with porous organic polymers (POPs) and highly porous microstructure support (HPμS) layers featuring regularly arranged columnar macrovoids formed by carefully adjusting the thermodynamic instability of a polymer solution. POPs were introduced into the active layer of an RO membrane to impart the water channel and hydrophilicity. POP fillers were functionalized with amine and sulfonic groups, and the synthesized POPs were introduced into different phases depending on sulfonation. Sulfonated POPs with high hydrophilicity provided additional water pathways and hydrophilic properties while maintaining the active layer's thickness, notably improving water permeability. Surprisingly, the simultaneous optimization not only enhanced the permselectivity further but also made thin-film nanocomposite (TFN) membranes overcome the trade-off because the shortened diffusion pathway by the HPμS was more beneficial for improving water permeability than salt permeability. As a result, the simultaneously optimized TFN exhibited 2.2 to 2.7 times higher water permeability and 2.6%p to 3.4%p higher salt rejection than a control TFC membrane.

Investigating the efficiency of a ceramic-based thin-film composite nanofiltration membrane for dyes removal

This study focuses on producing polyamide thin-film composite (TFC) ceramic membranes using interfacial polymerization, resulting in a polyamide layer on ceramic tubular substrates (Al2O3). These Al2O3 substrates possess robust mechanical and physical traits, featuring a porous surface structure. TFC membranes exhibit a thin, dense structure with root-like nanostructures on the ceramic base, with a thickness of around 260 nm. Atomic force microscopy confirms the smoother surface of TFC membranes with an average roughness value of 18 nm compared to ceramic tubular substrates. TFC membranes exhibit negative zeta potentials within a pH range of 4.7–10, while ceramic tubular substrates show more complex zeta potential behavior. Both substrate and TFC membranes are hydrophilic, with the TFC membrane having a slightly higher water contact angle (approximately 43 ± 1°). Zeta potential analysis reveals a negative potential of around −23 mV for the TFC membrane. In water permeability tests, the ceramic tubular substrate membrane demonstrates high permeability, whereas the TFC membrane displays slightly lower permeability (28 ± 0.8 L/m2 h bar) due to the presence of the polyamide selective layer. Importantly, the TFC membrane significantly enhances organic dye rejection compared to the ceramic tubular substrate, with rejection rates of 95% for CR, 92% for BTB, and 86% for MB. Rejection performance is mainly influenced by size exclusion and dye molecular charge. These novel TFC ceramic nanofiltration membranes offer improved water permeability while maintaining selectivity, holding promise for effectively removing organic pollutants in water treatment applications.

Fluorination as a powerful tool for improving water/salt selectivity of hydrophilic polyethersulfone

Fluorination is an important tool for tuning polymer free volume properties, but the effect of fluorination on the water/salt transport properties of desalting polymers remains uncertain. In this work, a series of novel cysteine-based polyethersulfones (PES-Cys and PES-Cys-2F, PES-Cys-6H and PES-Cys-6F, PES-Cys-8H, and PES-Cys-8F) were designed in pair (4,4'-difluorodiphenyl sulfone versus 3,3',4,4'-tetrafluorodiphenyl sulfone, bisphenol A versus hexafluorobisphenol A, and 4,4'-dihydroxybiphenyl versus decafluorobiphenyl). Upon casting into membranes via the solvent evaporation method, the membranes/polymers were characterized by 1H NMR, FTIR, XRD, DSC, Zeta potential, and the water/salt transport properties of the membranes was investigated systematically. It has been demonstrated that fluorination brings out greater spatial site resistance, stronger hydrophobicity, and higher electronegativity to polyethersulfone chains, leading to decreased water sorption but increased salt sorption. Fluorinated polyethersulfone displayed higher water diffusion coefficient because the C–F group can shatter water clusters into water molecules, which can diffuse more rapidly. Fluorinated polyethersulfone exhibit superior water/salt selectivity, with the most rigid PES-Cys-8F of the highest fluorine content showing water/salt selectivity over the empirical upper bound line. The enhanced water/salt selectivity is mostly because that fluorination improves water permeability by significantly increasing the water diffusion coefficient, while the electrostatic barrier provided by the electronegative fluorine atoms inhibits salt diffusion. This study provides valuable theoretical guidance for future molecular design of antioxidant desalting polymers.

Effect of pre-treated waste tire rubber on properties of concrete

In present day scenario the human activities have led to environmental degradation with increased urbanization contributing to many fold increase in constructing activities, which uses limited natural resources. Therefore, prevention of resource over-utilization and recycling of the waste is of utmost priority in construction sector. Waste tires rubber is one such potential material which can be used in concrete as replacement for fine aggregates replacement. This study represents the effect of addition of crumb rubber in concrete as sand replacement ranging from 5-20% on volume basis. The study evaluated the workability, compressive strength, ultrasonic pulse velocity (UPV), electrical resistivity and water permeability at 28 days. Tire rubber was also pre-treated with NaOH and KMnO4 as an effort to enhance its bonding characteristics. The contact angle was measure to test the efficacy of the treatment in reducing water hydrophobicity of crumb rubber. The treatment of tire rubber with NaOH and KMnO4 proved to be promising in regaining some of lost compressive strength and improved water permeability. However, both treatment processes didn’t have any significant effect on the workability. The NaOH treatment proved to be an overall better treatment than KMnO4 which was due to the reduced hydrophobicity as depicted by lower contact angle.

Regulation of micro-structure and surface property of SWRO membrane via introducing albumin into polyamide layer for improving permselectivity

The concerned trade-off effect between water permeability and permselectivity hinders further improvement of the performance based on dense polymeric membranes. Here, seawater reverse osmosis (SWRO) membranes with higher water-salt permselectivity and water permeability were prepared by introducing albumin concentrated and crystallized from chicken egg white (EW) into aqueous solution before interfacial polymerization (IP) to regulate the micro-structure and surface property of the aromatic polyamide layers. Due to the hydrophilic nature and its multi-functional groups, EW albumin could disperse homogeneously in aqueous solution during the interfacial polymerization process. The deposited EW albumin on polysulfone (PSf) substrate could also increase the surface charge as well as its hydrophilicity. Due to the higher and more vertical leaf-like structures, together with the rougher surfaces and more hydrophilic surface, the water flux of db-0.1 membrane increased by 21.29 % compared to the original db-0 membrane, which reached 49.66 L·m−2·h−1. Meanwhile, because of the higher cross-linking degree and the more negatively charged property, db-0.1 membrane which exhibited the best water permeability also showed the best NaCl rejection of 99.66 %. It provides new sights on simultaneous regulation of micro-structure and surface property of SWRO membranes for improving water permeability and permselectivity via a facile incorporation procedure.

Effect of MAX Phase Ti3ALC2 on the Ultrafiltration Membrane Properties and Performance

Membrane fouling remains a major obstacle to ultrafiltration. Due to their effectiveness and minimal energy demand, membranes have been extensively employed in water treatment. To improve the antifouling property of the PVDF membrane, a composite ultrafiltration membrane was created employing the in-situ embedment approach throughout the phase inversion process and utilizing a new 2D material, MAX phase Ti3ALC2. The membranes were described using FTIR (Fourier transform infrared spectroscopy), EDS (energy dispersive spectroscopy), CA (water contact angle), and porosity measurements. Additionally, atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), and energy dispersive spectroscopy (EDS) were employed. Standard flux and rejection tests were applied to study the produced membranes’ performance. Adding Ti3ALC2 reduced composite membranes’ surface roughness and hydrophobicity compared to the pristine membrane. Porosity and membrane pore size increased with the addition up to 0.3% w/v, which decreased as the additive percentage increased. The mixed matric membrane with 0.7% w/v of Ti3ALC2 (M7) had the lowest CA. The alteration in the membranes’ properties reflected well on their performance. The membrane with the highest porosity (0.1% w/v of Ti3ALC2, M1) achieved the highest pure water and protein solution fluxes of 182.5 and 148.7. The most hydrophilic membrane (M7) recorded the highest protein rejection and flux recovery ratio of 90.6, which was much higher than that of the pristine membrane, 26.2. MAX phase Ti3ALC2 is a potential material for antifouling membrane modification because of its protein permeability, improved water permeability, and outstanding antifouling characteristics.

Recovery of cleaning agents from clean-in-place (CIP) wastewater using nanofiltration (NF) and forward osmosis (FO)

This study proposed a Nanofiltration (NF) – Forward Osmosis (FO) membrane system to recover the cleaning agents from model dairy CIP wastewater. The NF steps consist of 4 kDa and 200 Da Nanofiltration (NF) membrane to reduce the lactose and whey protein before the forward osmosis (FO) concentration step. It was found that a series of NF filtration (4 kDa-200 Da) eliminated the lactose under detection level and protein by 96.3 %. The permeates from 4 kDa or 200 Da NF were further treated with FO. Two different FO membranes, cellulose triacetate (CTA) and thin-film composite (TFC). The increase of salts concentration from 0.5 M to 2.0 M increased the water flux from 17.8 LHM to 31.7 LHM when the TFC membrane was used. 4 times increase in the salts concentration did not result in the same magnitude increase in the water flux due to concentration polarization.. In addition, the TFC membrane was found to show an enhanced level of water flux compared to the CTA membrane over the same draw solution concentration due to improved water permeability. The TFC membrane with 2 M of NaCl was selected for further concentrating the NF permeates. Concentration using TFC FO membranes resulted in an increase the active alkali between 0.5% - 0.6%. The cleaning effectiveness of the recovered cleaning agents was assessed using Quartz Crystal Microbalance with Dissipation (QCM-D). The cleaning agents recovered by 4 kDa/200 Da NF and FO were found to present no significant difference as compared to fresh cleaning agents.

Surface Zwitterionization via Grafting of Epoxylated Sulfobetaine Copolymers onto PVDF Membranes for Improved Permeability and Biofouling Mitigation

Grafting of zwitterionic moieties has been shown to overcome the decrease in permeability after membrane modification. Herein, we report the grafting of epoxylated sulfobetaine (poly(glycidyl methacrylate-co-sulfobetaine methacrylate or poly(GMA-co-SBMA)) zwitterionic copolymers onto polyvinylidene fluoride (PVDF) surfaces to obtain superhydrophilic and superoleophobic membranes. The three-dimensionally modified membranes simultaneously exhibit excellent fouling resistance and hemocompatibility with improved water permeability during protein filtration. The zwitterionic moiety in the bulk membrane promotes the formation of a hydration layer, resulting in a dramatic reduction in hydrophobic interactions between the membrane and proteins or bacteria. Zwitterionic polymers establish a relatively electrically neutral surface through the presence of positive and negative charge groups on their pendant, leading to a reduction of adhesion between charged protein molecules and membranes. The modified PVDF surface exhibits very high hemocompatibility for human erythrocytes, platelets, and leukocytes. In the static fouling test, this biofouling hardly adhered to the membrane surface. The developed membrane has 3 times higher water permeability than the unmodified commercial membrane. It also showed a significant improvement in antifouling performance during dynamic fouling testing. Furthermore, flux regeneration of the modified membranes is easier to achieve by simple water recirculation compared to pristine PVDF membranes. Therefore, this study provides a promising way to develop antifouling membrane surface modification, which can be potentially used for bioseparation applications.