Water Nanofiltration Research Articles

Study of the structure and characterization of membranes reinforced with CuO-NPs/Graphene Oxide using bacterial cellulose extracted from Sargassum sp. for water nanofiltration system

Bacterial cellulose membranes find extensive applications in industries involving water purification, wastewater treatment, and biomedical uses. Nevertheless, prevailing membranes suffer from drawbacks like water flow hindrances and fouling susceptibility. Hence, the pressing need for more efficient and robust BC membranes. This study aims to assess the impact of a hybrid treatment involving Copper Oxide nanoparticles (CuO-NPs) and Graphene Oxide (GO) on bacterial nanocellulose membranes. The research employed two treatments: (1) control (BNCA), and (2) Bacterial cellulose infused with 0.5 wt% CuO-NPs/GO. The nanocellulose production involved a high-pressure homogenizer, followed by acetate nanocellulose synthesis and nanocomposite membrane functionalization with CuO nanoparticles. SEM, FTIR, and XRD analyses characterized the membranes. Successfully formed seaweed-derived bacterial cellulose had a thickness of 1-3 cm. Characterization showed it belonged to Cellulose type I with a crystalline degree ranging from 82.3% to 83.1%. FTIR analysis of dry BNCA membranes indicated changes in transmittance at 1738, 1554, and 764 cm-1 due to CuO-NPs/GO addition, altering the O-H bond in bacterial cellulose. Based on the results of the above research, it is evident that the Membrane Reinforced with CuO-NPs/Graphene Oxide has been successfully developed and holds potential as a water nanofiltration system.

Lindane removal by membrane nanofiltration

Lindane is the γ-isomer of 1,2,3,4,5,6-hexachlorocyclohexane (HCH) and it has been widely used in the pesticide industry due to its insecticide properties. In the production of lindane, significant quantities of other HCH isomers are generated as byproducts. All these compounds are typically stored in landfills, often with poor management practices. Polyamide membranes, two commercial membranes from Alfa Laval (NF99HF and NF99) and homemade thin film composite membranes prepared by interfacial polymerization on a porous polyimide support, were evaluated for water nanofiltration (NF) of HCH isomers, including lindane. Homemade membranes, with a lindane rejection of 91.3 % and a permeance of 2.7 L·m−2·h−1·bar−1, offered the highest performance in terms of both permeance and rejection. NF99 and homemade membranes were proven to be equally effective in removing α-HCH and β-HCH, showing similar results. Homemade membranes achieved 99.5 and 99.8 % rejections for α-HCH and β-HCH, respectively. Long-term experiments were carried out with NF99 and homemade membranes to assess their stability during filtrations with lindane solutions for up to 214 h. Homemade TFC membrane maintained its initial rejection (ca. 93.5 %) after 214 h, although its permeance decreased over time, ending in 2.5 L·m−2·h−1·bar−1.

New insights into the influence of pre-oxidation on membrane fouling during nanofiltration of brackish water considering inorganic-organic complexation and oxidant reduction byproducts

Even though pre-oxidation is usually considered as a promising method to alleviate membrane fouling, information on performance and inner mechanisms of pre-oxidation-influenced membrane fouling during nanofiltration of brackish water is still limited. This study is the first work in which oxidant reduction byproducts and interaction between different pollutants were particularly considered to address these problems. Herein, nanofiltration experiments with different pre-oxidized synthesis brackish water containing inorganic salts and organic pollutants were conducted. Membrane flux results showed that both NaClO and K2FeO4 aggravated membrane fouling, but 0.45 mg/mg TOC KMnO4 mitigated it when simulation results of NICA-Donnan model showed that the complexation between calcium ions and humic acid (HA) was weakened. However, membrane fouling was enhanced by higher dosage of KMnO4. Fourier transform infrared spectrometer using attenuated total reflection (ATR-FTIR) and X-ray diffraction (XRD) spectrum showed that the aggravated membrane fouling was mainly caused by the generation of amorphous manganese oxide, which was oxidant reduction byproduct and had strong capacity for adsorption of HA. Particle size distribution and zeta potential variation indicated that the accumulation of HA could enhance the crystallization process and then the electrostatic attraction between membrane and bulk crystallization was induced. According to SEM images and fitting results of Hermia's models, the already-formed bulk crystallization by 1.90 mg/mg TOC KMnO4 could deposit on membranes more easily, followed by the formation of a denser fouling layer. Overall, the present study provided new insights into the design of reliable pre-oxidation strategies for alleviating membrane fouling during nanofiltration of brackish water.

Novel insight into prior induced crystallization on brackish water nanofiltration

An ultrafiltration/nanofiltration system enhanced by induced crystallization was constructed. The aim of this study was to assess the feasibility and contribution of fouling mitigation during brackish water nanofiltration by prior induced crystallization at ultrafiltration stage. Induced crystallization and increased negative charge density caused by alkalization probably have a synergistic effect on nanofiltration (NF) scaling and fouling mitigation. The electron acceptor surface tension and water contact angle indicated that the NF membrane became more hydrophilic during the alkalization. And thus the influence of acid-base polar interactions on membrane fouling behavior was strengthened to increase the energy barrier, improved the anti-fouling capacity. The total cost of moderate alkalization was reduced to $ 0.18 per ton, indicated a great potential for practical application. Furthermore, the functional model between irreversible resistance with hydrogen ion concentration and membrane charge density was also created. This study developed a sustainable and economy approach for brackish water treatment.

Microfluidic preparation of thin film composite hollow fiber membrane modules for water nanofiltration: Up-scaling, reproducibility and MOF based layers

BackgroundThe commercialization of thin film composite (TFC) hollow fiber (HF) membranes remains challenging owing to issues associated with membrane manufacturing. MethodsTFC membranes were synthesized by microfluidic interfacial polymerization of polyamide (PA) on polysulfone hollow fiber (HF) membrane modules. A total of 33 HF membrane modules were prepared with different number of HFs (from 1 to 25) and different lengths (from 10 to 50 cm). They were evaluated in a nanofiltration operation in terms of water permeance and rose Bengal (RB) and MgSO4 rejections. Significant findingsAmong the 33 modules, 73% showed RB rejections higher than 95%, while 36% of the modules reached rejections above 99%. During the membrane synthesis, different parameters, such as PA monomer concentration, residence time and reaction time, were studied. As a result, the amount of monomer was reduced by ca. 80%. The versatility of microfluidics allowed incorporating hydrophilic metal-organic framework (MOF) ZIF-93 to produce HF modules with PA/MOF bilayered membranes (a continuous layer of MOF between the support and the PA film) which led to an important enhancement of the water permeance from 1.3 (bare PA membrane) to 5.3 L·m−2·h−1·bar−1 (PA/ZIF-93 HF membrane), maintaining RB rejection above 95%.

Hybrid Technology Seawater Desalination Based on Reverse Osmosis and Membrane Distillation Methods

The article presents the results of a computational and analytical study of hybrid RO–MD (Reverse Osmosis–Membrane Distillation) technologies for desalination of the Caspian Sea, providing for the production of an additional amount of desalinated water by the MD method from RO concentrates heated to 50–80°C due to waste heat of fuel combustion products in steam boilers. Two options for solving the problem of the formation of CaCO3 and CaSO4 precipitates on membranes were studied: with preliminary nanofiltration (NF) or Na-cationation (Na) of sea water, as an alternative to the use of antiscalants (AS) and acid. The negative environmental effect of most plants (eutrophication of water bodies) and their low efficiency at high concentrations of desalinated water are taken into account. The Langelier index (СаСО3) and the degree of concentrate saturation (СаSO4) were used as criteria for precipitation of deposits on the membranes. The NF and RO processes were studied using the ROSA computer program, and the MD and Na processes were studied by computer simulation of the corresponding calculation models. It was found that at a 70% permeate yield at the NF and RO stages, the possibility of calcium precipitation on the RO and MD membranes is prevented, but their precipitation on the NF membranes is predicted, which makes the use of AS forced. At the same time, additional permeate production at the MD stage from RO concentrates reaches 40% of the amount of permeate from RO stadium, and the electricity consumption in general according to the scheme is 1.88 kWh/m3. Reducing the calcium hardness of sea water to 50 µg-eq/dm3 by the Na-cationization method makes it possible to refuse both the use of AS and acidification with sulfuric acid with additional production of MD permeate – 27% relative to RO permeate. Electricity consumption rises to 2.5 kWh/m3. To use the known advantages of NF without the use of AS, a hybrid Na–NF–RO–MD scheme is proposed. It has been established that at 80% yields of NF and RO permeates, to prevent the formation of CaSO4 precipitates at all stages of treatment, it is sufficient to reduce the hardness of sea water from 16 to 5.5 m-eq/dm3, and by acidifying the softened water to exclude the formation of CaCO3 precipitates.

Drinking water nanofiltration with concentrate foam fractionation—A novel approach for removal of per- and polyfluoroalkyl substances (PFAS)

Per- and polyfluoroalkyl substances (PFAS) are recognized as persistent pollutants that have been found in drinking water sources on a global scale. Semi-permeable membrane treatment processes such as reverse osmosis and nanofiltration (NF) have been shown effective at removing PFAS, however, disposal of PFAS laden concentrate is problematic. Without treatment of the concentrate, PFAS is released into the environment. The present work examined a novel PFAS removal scheme for drinking water using NF filtration with treatment of the resulting NF concentrate via foam fractionation (FF) with and without co-surfactants. The NF-pilot removed 98% of PFAS from AFFF contaminated groundwater producing permeate with 1.4 ng L−1 total PFAS. Using FF resulted in ∑PFAS removal efficiency of 90% from the NF concentrate and with improved removal of 94% with addition of cationic co-surfactant. The resulting foamate composed approximately 2% of the NF feedwater volume and contained greater than 3000 ng L−1 PFAS or 41 times greater than the NF feedwater. Addition of the cationic co-surfactant to the FF process resulted in increased removal efficiency of the shorter chain PFAS, specifically 37% for PFPeA, 9% for PFHxA, and 34% for PFBS thus attaining 59%, 99% and 96% removal efficiency, respectively. PFOA, PFPeS, PFHxS, PFOS each attained 99% FF removal with or without co-surfactant addition.

Nanofiltration with polyamide thin film composite membrane with ZIF-93/SWCNT intermediate layers on polyimide support

Among current separation processes, nanofiltration (NF), besides its easy scalability, exhibits low energy consumption, environmental impact and footprint, being widely used for water treatment and solvent recovery. The development of membranes for NF involves perfecting the skin selective layer, the sublayers and the support. In this work, a multilayer structure membrane is presented where a selective layer of polyamide (PA, thickness 40–60 nm) was interfacially polymerized on a sub-layer of MOF ZIF-93 (thickness ∼ 50 nm) grown on another sub-layer of single-walled carbon nanotubes (SWCNT, thickness ∼ 400 nm) vacuum filtrated on an asymmetric polyimide P84® support (thickness ∼ 200 μm). The membrane with structure PA/ZIF-93/SWCNT/P84 showed excellent results in water NF and methanol organic solvent NF of different dyes (with the highest values of water and methanol permeances of up to 57.6 and 84.5 L·m−2·h−1·bar−1, respectively, with rejections usually greater than 99%). By means of a wide range of characterization techniques (contact angle, AFM, XRD, ATR-FTIR and FIB-SEM) the role of every component in the membrane was elucidated. In fact, the presence of the sublayer of ZIF-93 increased the roughness and hydrophilicity as well as decreased the thickness of the PA layer. These effects are related to the fact that the sublayers subordinate the interfacial polymerization as well as influence the properties of the PA film and therefore its NF performance, even showing chlorine resistance as well as ten-day cross-flow NF stability.

Poly(vinylidene fluoride) Substrate-Supported Polyamide Membrane for High-Temperature Water Nanofiltration

Conventional polysulfone and polyethersulfone membrane-supported polyamide (PA) nanofiltration (NF) membranes suffer an obvious performance decline due to the drastic pore shrinkage of their membranes during high-temperature (HT) desalination processes. Herein, a thermally stable PA NF membrane (PVDF-IP-2) was successfully constructed over a relatively hydrophobic polyvinylidene fluoride (PVDF) membrane using a continuous interfacial polymerization (CIP) method. The PVDF-IP-2 membrane had a moderate water permeance of 8.3 L m–2 h–1 bar–1 and a 99.7% Na2SO4 rejection at room temperature, which were comparable to those of commercial NF membranes. Introducing calcium ions (Ca2+) into the aqueous solutions further confined the transport rate of the piperazine monomer across the reaction interface through the coordination functions between Ca2+ and piperazine molecules, forming a high-flux (15.9 L m–2 h–1 bar–1 at room temperature) NF membrane (PVDF-IP-Ca) with an excellent Na2SO4 rejection (∼98.6%). Impressively, the PVDF-IP-Ca membrane presented an excellent antifouling behavior and performance stability during both fouling and high-temperature filtration tests. The Ca2+-assisted IP (Ca–CIP) strategy is expected to be a facile and universal approach to preparing TFC desalination membranes for HT environmental applications on relatively hydrophobic supports.

Effects of interlayer spacing and oxidation degree of graphene oxide nanosheets on water permeation: a molecular dynamics study.

Graphene oxide (GO) membranes have shown great potential in the applications of water filtration and desalination. The flow behavior and structural properties of water molecules through GO nanochannels are still under debate. In this work, molecular dynamics simulations were performed to explore the effects of interlayer spacing and oxidation degree of GO nanochannels on water transport. The results show that GO nanosheets have strong adsorption capacity. The adsorbed layer of water molecules on GO surface is thermodynamically stable and not easy to flow. When the interlayer spacing falls into the range of 0.6 ~ 1.0nm, water molecules form into single or double adsorbed layers between two GO nanosheets. When the interlayer spacing is bigger than 1.2nm, the other water layers in the middle of nanochannel become disordered. Taking the separation performance based on size exclusion into consideration, the most suitable interlayer spacing for water nanofiltration is approximate 1.2nm, which has one flowing layer of water molecules. Oxygen-containing groups are unfavorable for water permeation, as more and more hydrogen bonds prevent water flowing on GO surface with the increasing oxidation degree. Our simulation results may help to improve the design of GO nanofiltration membranes for water treatment.

Nanopumps without Pressure Gradients: Ultrafast Transport of Water in Patterned Nanotubes.

The extreme liquid transport properties of carbon nanotubes present new opportunities for surpassing conventional technologies in water filtration and purification. We demonstrate that carbon nanotubes with wettability surface patterns act as nanopumps for the ultrafast transport of picoliter water droplets without requiring externally imposed pressure gradients. Large-scale molecular dynamics simulations evidence unprecedented speeds and accelerations on the order of 1010 g of droplet propulsion caused by interfacial energy gradients. This phenomenon is persistent for nanotubes of varying sizes, stepwise pattern configurations, and initial conditions. We present a scaling law for water transport as a function of wettability gradients through simple models for the droplet dynamic contact angle and friction coefficient. Our results show that patterned nanotubes are energy-efficient nanopumps offering a realistic path toward ultrafast water nanofiltration and precision drug delivery.

Polyamide-MIL-101(Cr) Thin Films Synthesized on Either the Outer or Inner Surfaces of a Polysulfone Hollow Fiber for Water Nanofiltration.

High-performance thin film nanocomposite (TFN) hollow fiber (HF) membranes, with MIL-101(Cr) MOF nanoparticles (52 ± 13 nm) embedded, have been synthesized with the polyamide layer formed either on the outer or inner surface of a polysulfone HF (250 and 380 μm ID and OD, respectively). The TFN_out membrane was developed using the conventional interfacial polymerization method, typically applied to obtain TFN flat membranes (MOF particles added to the thin layer by deposition). This membrane gave a water permeance value of 1.0 ± 0.7 L·m–2·h–1·bar–1 and a rejection of 90.9 ± 1.2% of acridine orange (AO, 265 Da). In contrast, the TFN_in membrane was synthesized by microfluidic means and gave a significantly higher water permeance of 2.8 ± 0.2 L·m–2·h–1·bar–1 and a slightly lower rejection of 87.4 ± 2.5% of the same solute. This remarkable increase of flux obtained with small solute AO suggests that the HF membranes developed in this work would exhibit good performance with other typical solutes with higher molecular weight than AO. The differences between the performances of both TFN_in and TFN_out membranes lay on the distinct superficial physicochemical properties of the support, the synthesis method, and the different concentrations of MOF present in the polyamide films of both membranes. The TFN_in is more desirable due to its potential advantages, and more effortless scalability due to the microfluidic continuous synthesis. In addition, the TFN_in membrane needs much fewer quantities of reactants to be synthesized than the TFN_out or the flat membrane version.

Polyamide Nanofiltration Membranes from Emulsion-Mediated Interfacial Polymerization

Fabrication of nanofiltration (NF) membranes using interfacial polymerization (IP) continues to receive tremendous interest in research and development due to the broad applications of NF in water ...

High-performance nanofiltration membrane intercalated by FeOOH nanorods for water nanofiltration

Nanofiltration (NF) is considered a promising candidate to improve the separation efficiency in water desalination, and the membranes with incomparable water permeance and great selectivity are urgently requried to reduce the energy consumption. Iron oxohydroxides (FeOOH) nanorods, goethite (α-FeOOH) with a diameter of 30–40 nm and length of about 340 nm, were synthesized and deposited on PES microfiltration (MF) membrane with the pore size of 0.1 μm by the assistance of vacuum filtration. Then a high flux NF membrane intercalated by well-dispersed FeOOH nanorods was fabricated using piperazine (PIP) and trimesoyl chloride (TMC) as monomers. The influence of FeOOH deposition on the surface properties and the nanofiltration performance of the fabricated membranes was studied. XPS, SEM, TEM, AFM, water contact angle (WCA) and NF measurements were utilized to investigate membrane performance. The optimum membranes showed a high water permeability (34.1 L·m−2·h−1·bar−1), high rejection for Na2SO4 (95.0%) and good ion selectivity towards Cl−/SO42− (23.9). Furthermore, the optimized NF membranes are acid-stable to some extent, and showed good stability in long-term NF operations. This work presents a facile and low-cost strategy for constructing high performance NF membranes.

Selection of membranes and reagents for membrane facilities operation to treat ground water

Introduction. New techniques to operate reverse osmosis facilities are presented as well as problems and disadvantages are discussed that vodocanals face with, such as: imported chemicals, high operational costs, low reliability, concentrate handling and disposal. Main reasons that cause problems are understood. Experiments are described that provide evaluation of reagents efficiencies and ways to significantly decrease concentrate flows and reduce operational costs. A newly developed approach is presented that uses nanofiltration membranes and enables us to reduce chemical, energy and concentrate discharge costs. Goals — the investigation of antiscaling efficiencies together with use of membranes with different properties to reduce operational costs due to low chemical dosing, low pressure and energy consumption.
 Materials and methods. Experiments are conducted to evaluate inhibiting efficiencies using different antiscalant doses and different membranes. Experimental method is describe to calculate rates of calcium carbonate formation as a function of coefficient K (Initial Volume Reduction coefficient) value. To provide economical comparison of different water treatment techniques, operational costs are evaluated depending on operational parameters, such as: coefficient K, working pressure antiscalant dose values as well as membrane type used.
 Results. Main relationships are obtained of calcium carbonate scaling rates that provide chemical consumption, concentrate flow rate and power consumption. Using two ground water compositions examples are calculated to predict product water composition for different membranes and of feed water and product water flows. Operational costs are calculated for both cases.
 Conclusions. To reduce hardness of the ground water nanofiltration membranes can be efficiently applied that ensures low operational costs of membrane facility. Application of nanofiltration membranes possess lower scaling propensities and therefore enables us to use smaller doses of aniscalants added to feed water. Despite the increased amount of membrane elements required to furnish membrane facility, the total operational costs amount is lower due to lower chemical costs (antiscalants and cleaning agents), energy costs as well as payments for concentrate disposal.

Scaling Risk Assessment in Nanofiltration of Mine Waters.

Nanofiltration can be applied for the treatment of mine waters. One of the main problems is the risk of crystallization of sparingly soluble salts on the membrane surface (scaling). In this work, a series of batch-mode nanofiltration experiments of the mine waters was performed in a dead-end Sterlitech® HP 4750X Stirred Cell. Based on the laboratory results, the concentration profiles of individual ions along the membrane length in a single-pass industrial-scale nanofiltration (NF) unit was calculated, assuming the tanks-in-series flow model inside the membrane module. These calculations also propose a method for estimating the maximum achievable recovery before the occurrence of the calcium sulfate dihydrate scaling in a single-pass NF 40″ length spiral wound module, simultaneously allowing metastable supersaturation of calcium sulfate dihydrate. The performance of three membrane types (NF270, NFX, NFDL) has been evaluated for the nanofiltration of mine water.

Optimization of solar-driven systems for off-grid water nanofiltration and electrification

The work described is motivated by an inability to extend central infrastructure for power and water to low-population-density areas of the Navajo Nation and elsewhere. It is estimated that 35% of the Navajo population haul water for household use, frequently from unregulated sources of poor initial quality. The proposed household-scale, solar-driven nanofiltration (NF) system designs are economically optimized to satisfy point-of-use water purification objectives. The systems also provide electrical energy for a degree of nighttime household illumination. Results support rational design of multiple-component purification systems consisting of solar panels, a high-pressure pump, NF membranes, battery storage and an electrical control unit subject to constraints on daily water treatment and excess energy generation. The results presented are conditional (based on initial water quality, membrane characteristics and geography) but can be adapted to satisfy alternative treatment objectives in alternate geographic, etc. settings. The unit costs of water and energy from an optimized system that provides 100 gpd (1 gallon is 3.78 L) and 2 kWh/day of excess electrical energy are estimated at $0.16 per 100 gallons of water treated and $0.26 per kWh of nighttime electrical energy delivered. Methods can be used to inform dispersed infrastructure design subject to alternate constraint sets in similarly remote areas.

Nanofiltration thin‐film composite membrane on either the internal or the external surface of a polysulfone hollow fiber

AbstractThe inner and outer surfaces of a porous hollow fiber polysulfone support are compared as substrates for the synthesis of polyamide thin‐film composite (TFC) membranes by interfacial polymerization. While both surfaces have pores common of microfiltration membranes, the inner surface has a larger pore diameter than the outer surface (2,700 nm compared to 950 nm). The inner TFC membrane showed higher water nanofiltration permeance than the outer (2.20 ± 0.17 compared to 0.13 ± 0.03 L m−2 hr−1 bar−1). This was due to the influence of the porosity and roughness, which were different on both support surfaces. These membranes are interesting because they were synthesized in a hollow fiber support with a high membrane area per volume unit (~6,900 m2/m3) and the substrate used was commercial, which means that the TFC membrane obtained is suitable for industrial application. A mathematical simulation of the nanofiltration run with COMSOL Multiphysics 5.3 software confirmed the experimental trends observed.

The role of ferric coagulant on gypsum scaling and ion interception efficiency in nanofiltration at different pH values: Performance and mechanism

Nanofiltration (NF) is extensively applied after coagulation, which is conducive to alleviate organic fouling on NF membranes and improve water purification performance. However, inorganic fouling, which remains the major obstacle to limit the wider application of NF, could be enhanced by even low dosage coagulant. Few researchers realize the existence of coagulant-enhanced scaling, much less control it. This study investigated the effects of pH values on ferric-coagulant-influenced membrane performance during the nanofiltration of brackish water. Both membrane flux behavior (initial membrane flux, normalized flux during filtration, scaling resistance and scaling composition) and ion interception (filtrate conductivity and ions removal) were considered. Solution properties (zeta potential and nanoparticle size) were measured, and coagulant speciation variation was stimulated by Visual MINTEQ software. Mechanisms of ferric-coagulant-influenced membrane performance were analyzed from two aspects on the basis of correlation analyses: interface interaction on membrane surface and salts crystallization process (bulk crystallization and surface crystallization). Results showed that both bulk crystallization in feed solution and surface crystallization on membrane surface were dramatically induced by coagulant. Coagulant-enhanced fouling layer resistance decreased after the initial increase when pH varied from 3.0 to 10.0. Fe(OH)3, a kind of active ingredients in ferric coagulant, was highly responsible for the enhanced scaling layer resistance. Coagulant was found improving ionic removal under acidic conditions despite the fact that it could worsen removal under alkaline conditions. This study is of valuable reference to figure out the mechanisms of coagulant-influenced membrane performance and find a feasible approach to avoid membrane deterioration in coagulant-influenced NF process.

Impacts of monochloramine as an antifouling agent during nanofiltration (NF) of portable water

Impacts of monochloramine as an antifouling agent during nanofiltration (NF) of portable water